John Guest connectors for filtered and carbonated water in hospitality, hotels and offices: most common sizes and fittings
Many customers from bars, restaurants, hotels, offices, coffee shops, catering services, coworkings, gyms, hospitals and public spaces come to Install Beer looking for John Guest connectors to install, repair or expand professional systems for filtered water, chilled water, ambient water and sparkling water. In this sector, filters, reverse osmosis, chillers, carbonators, pumps, CO₂ regulators, taps, fountains and dispensers all coexist. The most common size is usually 3/8" OD for service water, with 1/4" OD on auxiliary lines, 1/2" OD for higher flow, and metric sizes such as 8 mm, 10 mm, 12 mm or 15 mm depending on the equipment and manufacturer.
Quick summary
In professional water dispensing, the most common size is usually 3/8" OD, especially between filter, cooler, carbonator, dispenser and tap. 1/4" OD appears in auxiliary lines, reverse osmosis, control, small filters, taps and drains. 1/2" OD is used when more flow or supply to several points is needed. In European equipment you also find 8 mm, 10 mm, 12 mm and 15 mm. For carbonated water you must always distinguish between the water circuit, the CO₂ circuit, the carbonator inlet, the carbonated water outlet and the final connection to the tap.
The key idea: filtered water and carbonated water are not the same line
In a professional installation there may be mains water, filtered water, chilled water, carbonated water, a CO₂ line, reverse osmosis reject water, chiller outlet and carbonator outlet. Although the tubes and fittings may look similar, each circuit can operate with a different pressure, gas, flow rate, temperature and material. Before buying a John Guest fitting, you must first identify the exact section of the installation.
This article complements the John Guest range and AquaTaps solutions
This guide helps identify sizes, fittings and adapters used in professional dispensing of filtered, chilled and carbonated water. To buy specific parts, check stock or search for connectors by format, see the John Guest fittings collection and the connectors and fittings category. If you are looking for a complete filtered, chilled or sparkling water solution for hospitality, office or home, also check AquaTaps and the water dispensers collection.
Downloadable John Guest catalogue for beverages and water dispensing
To identify John Guest fitting references, sizes and families used in beverage dispense, water treatment, filters, coolers, carbonators and professional HORECA systems, we have added the JG Drinks Dispense technical catalogue as a downloadable resource.
This document is especially useful for reviewing push-fit connectors in inch and metric sizes, fittings for 1/4", 3/8", 1/2", 5/16", 8 mm, 10 mm, 12 mm tubing and other sizes, as well as threaded adapters, valves, check valves, reducers, clips, accessories and food-grade tube for filtered water, carbonated water, on-tap drinks and professional equipment installations.
Guide contents
- What is used in HORECA water and offices
- What a filtered and carbonated water installation looks like
- Most common sizes
- Why the 3/8" tube dominates
- When 1/4" tubing appears
- When 1/2" tube appears
- 8 mm, 10 mm, 12 mm and 15 mm
- Carbonated water: CO₂, carbonator and fittings
- BSP, NPTF and equipment connections
- Which John Guest range to use
- List of the most common connectors
- Which fitting to use in each area
- How to install push-fit fittings
- Recommended spare parts kit
- Common mistakes
- What to buy at Install Beer
- Frequently asked questions
What is used in professional water dispensing
Professional water dispensing combines several technologies: filtration, dechlorination, reverse osmosis, chilling, carbonation, pumping, food-grade CO₂, service taps, fountains, bottle filling, ice machines, vending, coffee and mains connection. That’s why you’ll find a mix of inch and metric fittings, threaded connections, valves, check valves, reducers and hose adapters.
In hospitality and offices, 3/8" OD tubing is one of the most common sizes because it offers a practical balance between flow, flexibility, fitting availability, and compatibility with filters, chillers, carbonators, and dispensers. 1/4" OD is more associated with control, fine filtration, osmosis, and lower‑flow sections; and 1/2" OD appears when the equipment needs a higher water throughput.
Main size in many professional installations of filtered, cold, carbonated water and under-counter dispensers.
Common in osmosis systems, compact filters, drainage, control, auxiliary taps and low-flow lines.
Useful for higher flow, specific units, supply lines, chillers, taps or European manufacturers.
What a filtered and carbonated water installation looks like
A professional water installation can be simple, with a filter and tap, or more complex, with filtration, chiller, carbonator and multi-way tap for chilled, ambient and carbonated water. In HORECA projects, the design must be planned for flow rate, hygiene, maintenance, technical access and service continuity.
| Section of the installation | Function | Common sizes | Common fittings |
|---|---|---|---|
| Mains inlet | Feeds the system from the premises’ water supply. | 3/8" BSP, 1/2" BSP, 3/4" BSP, 3/8" OD, 1/2" OD, 10 mm, 15 mm. | BSP adapters, shut-off valve, tee, reducer, union and tube-to-hose fitting. |
| Filtration | Reduces sediment, chlorine, tastes, odours and protects downstream equipment. | 1/4", 3/8", 1/2", 10 mm. | NPTF/BSP adapters, elbows, unions, valves and clips. |
| Reverse osmosis | Reduces dissolved salts and adjusts water quality in certain projects. | 1/4" and 3/8". | Unions, elbows, tees, valves, restrictor, reducers and plugs. |
| Cooler | Chills the water before the tap or before carbonation. | 3/8", 1/2", 10 mm, 12 mm. | Straight connector, elbow, threaded adapter, valve, check valve. |
| Carbonator | It mixes cold water with CO₂ to produce carbonated water. | 3/8", 1/2", 8 mm, 10 mm, 12 mm depending on the unit. | Adapters, elbows, valves, check valves, water connectors, and CO₂ connectors. |
| CO₂ line | Feeds the carbonator with food-grade gas from the cylinder/regulator. | 1/4", 5/16", 3/8", 6 mm, 8 mm depending on the regulator and equipment. | Fittings compatible with inert gas, check valve, and tubing suitable for CO₂. |
| Carbonated water outlet | Carries carbonated water from the carbonator to the tap or tower. | 3/8", 10 mm, or the unit’s own size. | Unions, elbows, check valves, adapters to tap and compatible food-grade tubing. |
| Tap or font | Serves chilled, ambient, filtered or sparkling water to the user. | 5/16", 3/8", 8 mm, 10 mm, specific thread or JG cartridge. | Tap adapter, female connector, cartridge, hose or specific fitting. |
Most common sizes in HORECA water, hotels and offices
The following table summarizes the sizes most frequently found in professional water systems for HORECA, hotels, offices, and premises open to the public. The recommendation is always to measure the outer diameter of the tube and confirm whether the part to be connected is tube, thread, hose, or a proprietary connection on the unit.
| Size | Where it appears | Usual use | What to order |
|---|---|---|---|
| 3/8" OD | Filters, coolers, carbonators, dispensers, taps, fountains, ice machines and carbonated water units. | Main water line in many compact professional systems. | John Guest fittings for 3/8" OD tubing. |
| 1/4" OD | Reverse osmosis, auxiliary lines, control, taps, indicator lights, post-filters, tanks, drain and accessories. | Low-flow filtered water or internal connections. | John Guest fittings for 1/4" OD tubing. |
| 1/2" OD | Higher-flow equipment, feeds, some dispensers, branches and imported systems. | Greater water flow or supply to several points. | John Guest fittings for 1/2" OD tubing. |
| 5/16" OD | Some taps, towers, water, coffee, beverages and dispensing equipment. | Common intermediate size in beverage and water. | 5/16" fittings, do not confuse with 8 mm without checking. |
| 8 mm | European units, water taps, CO₂, reducers, dispensers and compact lines. | Water or gas depending on application and equipment. | 8 mm metric fittings. |
| 10 mm | European equipment, higher‑flow water, filters, chillers, carbonators and dispensers. | Water inlet or outlet with a higher flow rate than 8 mm. | 10 mm metric fittings. |
| 12 mm | Some water installations, supplies, HORECA equipment or transitions from plumbing. | Higher flow rate or technical adaptation. | 12 mm metric fittings. |
| 15 mm | Plumbing, supplies, cold/hot water, main runs and mains connection. | Water inlet or transition to a more conventional network. | 15 mm fittings or adapters to BSP. |
| 3/8" BSP | Angle valves, braided hoses, taps, filters and European outlets. | Connection to mains or to threaded equipment. | BSP adapter to 1/4", 3/8" or metric tubing depending on the installation. |
| 1/2" BSP | Taps, filters, filter housings, chillers, carbonators, equipment inlets and plumbing. | Standard hydraulic connection in many European installations. | 1/2" BSP adapter to push-fit tube. |
| 3/4" BSP | Large filters, heads, dishwasher/washing machine connections, supplies, and some equipment. | Supply from a larger thread or connection to equipment. | 3/4" BSP adapter depending on tubing and gasket. |
| 1/4" NPTF / 3/8" NPTF | Filter heads, imported units, valves, pressure gauges and accessories. | Adaptation to American-origin or OEM equipment. | NPTF male or female adapter depending on the piece. |
Do not confuse 3/8" with 10 mm or 1/2" with 12 mm
3/8" is approximately 9.52 mm and 1/2" is approximately 12.7 mm. Even if they look like 10 mm or 12 mm, in push-fit fittings that difference can cause leaks, poor insertion or disconnection. If the tube is imperial, use an imperial fitting; if it is metric, use a metric fitting.
Why 3/8" tubing is so common in professional water systems
3/8" OD tubing is a very widespread size because it allows a higher flow than 1/4" without taking up as much space as 1/2". In bars, offices, hotels and water coolers, it is usually enough to feed filters, compact chillers, carbonators, dispensers and taps for filtered, chilled or carbonated water.
- Inlet and outlet of compact professional filters.
- Water cooler supply.
- Connection to carbonated water carbonators.
- Outlet to tap or water column.
- Ice machines and vending.
- Water dispensers for offices.
- 3/8" straight union.
- 3/8" elbow.
- 3/8" tee.
- 3/8" shut-off valve.
- 3/8" check valve.
- 3/8" to 1/4" reducer.
- 3/8" x 1/4" NPTF adapter.
- 3/8" x 1/2" BSP adapter.
When 1/4" tubing appears in HORECA water systems
1/4" OD tubing appears in lower-flow lines: reverse osmosis, connection to auxiliary tap, pressurized tanks, drain, post-filters, small valves, equipment control and some treatment systems. In HORECA it is not usually the main line when large volumes are needed, but it is still essential in auxiliary components.
| Use of 1/4" | Why it is used | Common fittings |
|---|---|---|
| Reverse osmosis | The permeate and internal connections usually have a reduced flow. | Union, elbow, tee, valve, plug and tap connector. |
| Drain or reject | Carries reject or purge water from the system. | Elbows, unions, adapters and specific clips. |
| Auxiliary tap | Supplies a low-flow consumption point. | Tap connector, UNS, NPTF or compression adapter. |
| Control or sensors | Small branches for equipment or monitoring. | Union, T, valve and reducer. |
| Small filters | Compact or domestic units installed in offices. | NPTF adapters, elbows, and valves. |
When 1/2" tubing appears in professional water dispensing
1/2" OD tube appears when the system requires higher flow, lower pressure drop or supply to several units. It can also appear in imported installations, water lines to large coolers, higher-capacity carbonators or distribution to several taps.
Practical recommendation
If the unit has a low flow rate, 1/4" may be enough. If it is a professional dispenser, 3/8" is usually the practical standard. If there are several points, consumption peaks, bottle filling or high-volume carbonation, it may make sense to consider 1/2", 10 mm, 12 mm or 15 mm depending on the unit.
8 mm, 10 mm, 12 mm and 15 mm in European units
In Europe it is common to find equipment that does not work in inches but in metric. Many taps, regulators, coolers, towers, reducers, carbonated water systems or HORECA components may use 8 mm, 10 mm, 12 mm or 15 mm.
| Metric size | Close equivalent | Where it appears | Tip |
|---|---|---|---|
| 6 mm | Close to 1/4" but not the same. | Control, small equipment, gas, compact filters. | Do not swap with 1/4" without confirming. |
| 8 mm | Close to 5/16". | Water, CO₂, taps, regulators, columns, and European equipment. | Very common in HORECA; measure before buying. |
| 10 mm | Close to 3/8" but not the same. | Higher-flow water, filters, coolers, carbonators and dispensers. | Do not confuse with 3/8". |
| 12 mm | Close to 1/2" but not the same. | Supplies, water, coolers and some technical systems. | Do not confuse with 1/2" OD. |
| 15 mm | Metric plumbing measurement. | Mains inlet, main runs, cold/hot water, and transition to equipment. | Useful in installations closer to traditional plumbing. |
Carbonated water: CO₂, carbonator and John Guest fittings
Professional sparkling water is obtained by dissolving food-grade CO₂ in cold, filtered water using a carbonator. For the system to work well, water quality, pressure, temperature, flow rate, and connections must be correctly sized. A poorly connected installation can lose carbonation, generate irregular flow, cause leaks, or damage components.
- Mains inlet.
- Pre-filter or pre-treatment.
- Chiller, if the unit requires it.
- Water inlet to the carbonator.
- Sparkling water outlet to tap.
- Shut-off valves and check valves.
- Food-grade CO₂ cylinder.
- Pressure regulator.
- Tubing compatible with gas.
- Fittings compatible with inert gas.
- CO₂ inlet to the carbonator.
- Non-return or safety valve if the unit requires it.
| Section in sparkling water | Common sizes | Common fittings | Technical caution |
|---|---|---|---|
| Water inlet to the filter | 3/8", 1/2", 10 mm, 12 mm or 15 mm. | Valve, union, BSP/NPTF adapter, T. | Check mains pressure, flow rate and compatibility with the filter. |
| Filter outlet to chiller | 3/8" or 10 mm common. | Straight connector, elbow, tee, shut-off valve. | Avoid constrictions before the unit. |
| Water inlet to the carbonator | 3/8", 1/2" or metric depending on the equipment. | Adapters, valves, check valves, elbows. | Check the carbonator manual and flow direction. |
| CO₂ line | 6 mm, 8 mm, 1/4", 5/16" or 3/8" depending on regulator. | Fittings compatible with inert gas and pressure. | Do not use any random water fitting if it is not compatible with gas. |
| Carbonated water outlet | 3/8", 10 mm, or the unit’s own size. | Unions, elbows, check valves and tap adapters. | Preserve pressure and avoid loss of carbonation. |
| Sparkling water tap or column | 5/16", 3/8", 8 mm, 10 mm, or specific thread. | Tap adapters, female connectors, hose or JG cartridge. | Confirm the exact connection of the tap or spout. |
| Drain, overflow, or purge | 1/4", 3/8" or hose depending on equipment. | Adapter, elbow, tube-to-hose and clamp if applicable. | Do not confuse the drain with the drinking water line. |
Important warning about CO₂
CO₂ is not water. Although some John Guest ranges may be suitable for potable liquids and inert gases, pressure, material, gasket, compatible tube, and specific application must be confirmed. In sparkling water installations, it is not advisable to replace gas fittings, reducers, check valves, or carbonator connections without reviewing technical compatibility.
BSP, NPTF and common connections in HORECA
In hospitality, European, Italian, British, American, and OEM equipment are mixed. Therefore, BSP, BSPT, NPTF threads, tap threads, filter threads, carbonator connections, and hose adapters appear.
| Thread or connection | Where it appears | Usual use | Warning |
|---|---|---|---|
| 1/4" NPTF | Filter housings, heads, valves, pressure gauges and imported units. | Adapt 1/4", 3/8", or 1/2" tubing to American thread. | Do not mix with BSP. |
| 3/8" NPTF | Higher-flow filters, OEM equipment and imported accessories. | Larger-bore threaded connection. | Identify before assembling. |
| 3/8" BSP | Angle valves, taps, filters, hoses, and plumbing. | Connect to network or European equipment. | Confirm male/female and seal. |
| 1/2" BSP | Taps, filters, chillers, carbonators, plumbing and outlets. | One of the most common threaded connections. | It is not 1/2" OD tube. |
| 3/4" BSP | Large filters, equipment inlets, dishwasher connections or supplies. | Higher flow rate or connection to an existing supply point. | May require a flat gasket. |
| Hose tail | Pumps, chillers, ice machines, older units, or retrofits. | Transition from rigid tube to flexible hose. | Check the hose’s internal diameter. |
| John Guest tap cartridge | Taps, towers and water spouts for HORECA. | Direct connection to a specific size, for example 5/16", 3/8", or 8 mm. | Measure the exact tap connection. |
Which John Guest range to use in professional water dispensing
John Guest has several ranges. The choice depends on whether we are working with cold drinking water, intermittent hot water, inert gas, CO₂, imperial tube, metric tube, stainless steel, a filter, chiller or carbonator.
| Range | Usual colour | Typical use | When it fits |
|---|---|---|---|
| PI Grey Acetal | Gray | Potable liquids, dispensing, beverages, inert gases and imperial systems. | Very common in HORECA for 1/4", 3/8" and 1/2", especially for beverages, water and CO₂ if the application is compatible. |
| PP White Polypropylene | White | Drinking water, filtration, reverse osmosis, water treatment and pure water. | Very useful in filtration, osmosis, and water treatment. It should not be assumed for CO₂ if the datasheet does not allow it. |
| PM Metric Acetal | Black | Metric sizes, liquids, and inert gases depending on the application. | Useful for 6, 8, 10, 12, 15 and 22 mm in European equipment. |
| CI White Acetal | White | Water industry, drinking liquids and BSPP connections. | It may appear in tap connectors and water applications. |
| Superseal | Gray | Metal tubing, stainless steel, or applications requiring greater mechanical safety. | Useful in chillers, coils, or sections with stainless steel. |
| Accessories | Various | Clips, collet covers, plugs, tube cutters, bulkhead fittings and protective springs. | Essential for clean, safe, and maintainable installations. |
List of the most common John Guest connectors for filtered and carbonated water HORECA
The following table compiles the most common connectors for filtered, chilled and sparkling water systems, chillers, carbonators, fountains, dispensers, hotels, offices and HORECA. References may vary by market, color, range, suffix and availability, so they should be used as technical guidance.
| Connector or accessory | Common size | Indicative references | Typical professional use | Priority |
|---|---|---|---|---|
| Straight equal union | 3/8" x 3/8" | PI0412S / PP0412W | Join or repair water lines between filter, cooler, carbonator, and tap. | Very high |
| Equal 90° elbow | 3/8" x 3/8" | PI0312S / PP0312W | Turns under the counter, inside chillers, fountains, carbonators or technical cabinets. | Very high |
| Equal T | 3/8" x 3/8" x 3/8" | PI0212S / PP0212W | Branch a line to a tap, cooler, filter, carbonator or dispenser. | Very high |
| Shut-off valve | 3/8" | Depending on PI/PP/ASV range | Isolate the filter, chiller, carbonator, tap or equipment. | Very high |
| Non-return valve | 3/8" | Depending on the range available | Prevent water from flowing back towards the filter, pump, carbonator or mains. | Very high |
| Straight reducer | 3/8" x 1/4" | PI201208S / PP201208W | Go from a 3/8" main line to a 1/4" branch. | Very high |
| Reducing elbow | 3/8" x 1/4" | PI211208S / PP211208W | Reduce and turn in compact spaces. | High |
| Male NPTF adapter | 3/8" tube x 1/4" NPTF | PI011222S | Connect to filter head, valve, pressure gauge or imported equipment. | High |
| Male NPTF adapter | 3/8" tube x 3/8" NPTF | PI011223S | Connection to filter, carbonator, or OEM unit with a larger thread. | Medium‑high |
| Male swivel elbow | 3/8" tube x 1/4" or 3/8" NPTF/BSPT | PI091202S / PI091203S | Angled outlet on filters, chillers, carbonators, or equipment with limited space. | High |
| Female BSP adapter | 3/8" tube x 1/2" BSP | PI451214FS / variants | Connect to a tap, braided hose, chiller, or accessory with male thread. | High |
| Female BSP adapter | 3/8" tube x 3/8" BSP | PI451213S / variants | Connect to a stop valve, tap or unit with 3/8" male thread. | Medium‑high |
| Bulkhead / bulkhead fitting | 3/8" | PI1212S / PP1212W | Passing through panels, furniture, housings, or technical areas. | Medium |
| 2‑way splitter | 3/8" | PI2312S / PP2312W | Split one line into two water outlets. | Medium‑high |
| 3-way divider | 1/2" inlet x 3/8" outlets or multiple 3/8" | PI491612S / PI491212S | Distribution to several service lines. | Medium‑high |
| End stop / plug | 3/8" | PI0812S / PI4612S | Temporarily blind off a line during maintenance. | High |
| Straight equal union | 1/4" x 1/4" | PI0408S / PP0408W | Repair auxiliary lines, reverse osmosis or compact filters. | High |
| Equal 90° elbow | 1/4" x 1/4" | PI0308S / PP0308W | Turns in small equipment, osmosis systems or auxiliary taps. | High |
| Equal T | 1/4" x 1/4" x 1/4" | PI0208S / PP0208W | Branching in low‑flow lines. | Medium‑high |
| Shut-off valve | 1/4" | Depending on PI/PP/ASV range | Isolate tank, auxiliary tap, reverse osmosis unit, or control line. | High |
| Straight equal union | 1/2" x 1/2" | PI0416S | Higher-flow lines, supply to several points or imported systems. | Medium‑high |
| Equal 90° elbow | 1/2" x 1/2" | PI0316S | Bends in larger-bore lines. | Medium |
| Straight reducer | 1/2" x 3/8" | PI201612S | Go from a large supply line to a standard professional line. | High |
| Tube-to-hose fitting | 3/8" to 1/4", 5/16", 3/8" or 1/2" hose | PI251208S / PI251212S / PI251216S | Transition between rigid tube and flexible hose. | Medium‑high |
| Equal metric connector | 8 mm, 10 mm, 12 mm, or 15 mm | PM0408E / PM0410E / PM0412E / PM0415E | European equipment, taps, water, inert gas or metric lines. | High |
| Metric elbow | 8 mm, 10 mm, 12 mm, or 15 mm | PM0308E / PM0310E / PM0312E / PM0315E | Turns in metric installations. | High |
| Metric T | 8 mm, 10 mm, 12 mm, or 15 mm | PM0208E / PM0210E / PM0212E / PM0215E | Branches in metric systems. | Medium‑high |
| Metric male BSP adapter | 8, 10, 12 or 15 mm x BSP | PM011013E / PM011214E / PM011514E | Connect metric tube to European thread. | High |
| Safety clip | 1/4", 3/8", 1/2", 8 mm, 10 mm, 12 mm, 15 mm | PIC1808R / PIC1812R / PIC1816R / metric variants | Prevent accidental disconnections and identify lines. | High |
| LLDPE tubing | 1/4", 3/8", 1/2", 8 mm, 10 mm, 12 mm, 15 mm | Depending on colour and coil | Replace lines, expand the unit or repair leaks. | Very high |
| Tube cutter | Up to 12 mm or 22 mm depending on the model | JG-TS / TSNIP | Make a straight cut and avoid leaks. | Essential |
Looking for a specific size for a professional filtered or sparkling water system?
At Install Beer, we are official John Guest distributors in Spain and can help you identify the correct fitting if you have a photo, the outer tube measurement, the type of thread, and the equipment you want to connect: filter, cooler, carbonator, CO₂ regulator, tap, fountain, dispenser, ice machine, or HORECA installation.
See John Guest connectors Check compatibilityWhich fitting to use in each area of the system
A professional water system can include mains inlet, pre‑filtration, osmosis, tank, pump, chiller, carbonator, CO₂ line, tap, column, fountain, bottle filler and drain. Each zone may require a different fitting.
| System area | Common connectors | Common sizes | Practical tip |
|---|---|---|---|
| Mains inlet | BSP adapter, shut-off valve, tee, reducer, tube-to-hose adapter. | 3/8" BSP, 1/2" BSP, 3/4" BSP, 3/8", 1/2", 10 mm, 15 mm. | Confirm network pressure, flow rate, and type of connection. |
| Filter or prefiltration | NPTF/BSP adapters, elbows, unions, valves and clips. | 1/4", 3/8", 1/2", 10 mm. | Do not force plastic threads on filter housings or heads. |
| Reverse osmosis | Unions, elbows, tees, valves, reducers 3/8" to 1/4". | 1/4" and 3/8". | Respect inlet, permeate, reject and flow direction. |
| Water chiller | Union, elbow, threaded adapter, shut-off valve, non-return valve. | 3/8", 1/2", 10 mm, 12 mm. | Avoid choking the inlet flow. |
| Carbonator | Adapters, elbows, check valves, valves, CO₂ line. | 3/8", 1/2", 8 mm, 10 mm depending on the unit. | Differentiate water circuit and gas circuit. |
| Food‑grade CO₂ | Fittings compatible with gas, suitable tubing, valve and check valve. | 1/4", 5/16", 3/8", 6 mm or 8 mm. | Check pressure, regulator and technical compatibility. |
| Carbonated water outlet | Union, elbow, check valve, tap adapter and food-grade tube. | 3/8", 10 mm, or the unit’s own size. | Maintain pressure and avoid long or hot runs. |
| Tap or font | Tap adapter, JG cartridge, hose, elbow, valve. | 5/16", 3/8", 8 mm, 10 mm, 1/2" thread or proprietary connection. | Measure the exact connection of the tap. |
| Water cooler or dispenser | Union, elbow, tee, valve, reducer and clip. | 3/8", 1/4", 1/2", 8 mm, 10 mm. | Check the manufacturer’s manual. |
| Ice machine | Valve, inlet adapter, straight connector, reducer, and filter. | 1/4", 3/8", or specific thread. | Check pressure, filtration, and the equipment warranty. |
| Leak repair | Straight union, elbow, plug, tube cutter and length of tube. | The exact size of the damaged line. | Cut a new, straight section; do not reuse chewed-up tubing. |
How to correctly install a John Guest push-fit fitting
Most leaks in push-fit fittings are not due to the fitting itself, but to a bad cut, oval tube, tube not fully inserted, burrs, lateral stress, forced thread, incorrect seal, or wrong size.
1. Shut off the water or depressurize
Close the shut-off valve, switch off the pump or unit and release pressure before dismantling any connection.
2. Identify whether it is water or CO₂
For carbonated water, confirm whether the line is filtered water, carbonated water or CO₂.
3. Measure the tubing on the outside
Use a gauge if possible. Differentiate 1/4", 3/8", 1/2", 8 mm, 10 mm, 12 mm, and 15 mm.
4. Cut straight
Use a tube cutter. A crooked cut can damage the O-ring and cause leaks.
5. Remove burrs
The tube must be clean, with no deep scratches, crushing or deformation.
6. Insert until it stops
Push the tube straight all the way into the fitting. Do not leave it halfway in.
7. Strip to verify
Check that the clip has gripped the tube and that it does not come loose.
8. Fit the clip if applicable
In areas with vibration, pressure, movement or difficult access, a clip helps prevent accidental disconnections.
9. Open the water or gas in a controlled way
Perform a leak test with pressure before closing the technical cabinet or putting the equipment into service.
10. Check after the first service
In HORECA installations, it’s advisable to check connections after the first few hours of use.
Useful photo to identify the fitting
To choose correctly, prepare a clear photo of the old fitting, a photo of the unit where it is connected, the outside measurement of the tube with a caliper and, if there is a thread, a photo of the thread or the unit manual. This helps avoid confusing 1/4", 3/8", 1/2", 8 mm, 10 mm, BSP, NPTF, hose, tap cartridge, water or CO₂.
Recommended John Guest spare parts kit for filtered and carbonated HORECA water
A small selection of fittings can solve many issues in a restaurant, hotel, office or public space: leaks from a cut tube, filter changes, chiller replacement, connection to a carbonator, tap repair, work on the CO₂ line or adaptation between sizes.
| Item | Recommended quantity | Function |
|---|---|---|
| 3/8" straight connector | 3-5 units | Repair or extend main water lines. |
| 3/8" elbow | 3-5 units | Solve turns under the bar or in a technical cabinet. |
| 3/8" T | 2 units | Create branches to units or taps. |
| 3/8" shut-off valve | 2–4 units | Isolate filter, chiller, carbonator or tap. |
| 3/8" non-return valve | 1–2 units | Avoid unwanted returns in filtered or carbonated water. |
| 3/8" to 1/4" reducer | 2 units | Adapt auxiliary or control lines. |
| 1/4" straight union | 2 units | Repair reverse osmosis, drain or small filter lines. |
| 1/2" straight connector | 1–2 units | Repair higher‑flow supplies. |
| Fittings for the CO₂ line | Depending on regulator and carbonator | Connect food-grade gas using compatible tubing and fittings. |
| BSP/NPTF adapters | Depending on the equipment | Connect to filters, taps, coolers or carbonators. |
| Safety clips | Various | Prevent accidental disconnections and identify lines. |
| 3/8" and 1/4" LLDPE tubing and CO₂ size | Short sections or small coil | Replace damaged sections or extend the installation. |
| Tube cutter | 1 unit | Make straight cuts and prevent leaks. |
Common mistakes when buying John Guest connectors for professional water
| Error | Consequence | How to avoid it |
|---|---|---|
| Confusing 3/8" with 10 mm | The tube may not fit properly or it may leak. | Measure the actual outside diameter. |
| Confusing 1/2" with 12 mm | Unsafe or incompatible connection. | Differentiate imperial and metric sizes. |
| Mixing up tube with thread | An incorrect adapter is purchased. | Confirm whether it is OD, BSP, BSPT, NPTF or hose. |
| Not distinguishing between filtered water, carbonated water and CO₂ | Risk of incompatibility in pressure, material or operation. | Identify the circuit before replacing a fitting. |
| Mixing BSP with NPTF | Damaged thread or leak. | Identify the standard before tightening. |
| Reusing marked or deformed pipe | The O-ring may not seal. | Cut a new, straight section. |
| Do not use a tube cutter | Crooked cut, burrs and leaks. | Use a John Guest pipe cutter or suitable tool. |
| Over‑tightening plastic threads | Cracks or breakage of the filter housing or unit. | Tighten appropriately and use a compatible gasket. |
| Do not install shut‑off valves | Maintenance becomes slow and forces you to shut down more of the installation than necessary. | Section off filter, chiller, carbonator and tap. |
| Not using a check valve where required | There may be returns to the filter, carbonator or mains. | Review equipment diagram and installation regulations. |
| Do not leave technical access. | Maintenance becomes slow and expensive. | Leave access panels and fittings accessible. |
| Using fittings that are not suitable for drinking water or gas | Health risk, leak or incompatibility. | Use components suitable for drinking water, dispensing or CO₂ depending on the circuit. |
What to buy at Install Beer for professional dispensing of filtered and sparkling water
Install Beer works with John Guest every day in real beverage, water, filtration, dispensing, CO₂, and technical systems installations. For hospitality, hotel, office, and HORECA clients, the most useful selection is usually concentrated on 3/8", 1/4", 1/2" fittings, threaded adapters, valves, check valves, reducers, LLDPE tube, clips, tube cutters, and parts compatible with sparkling water and CO₂ when the circuit requires it.
| Need | Recommended product | Internal link |
|---|---|---|
| View the full John Guest range | Push-fit fittings, valves, adapters, pipes and accessories. | John Guest collection |
| Search fittings by type | Elbows, tees, unions, reducers, check valves and adapters. | Connectors and fittings |
| Replace professional water tubing | Food-grade and LLDPE tubing compatible with water or beverages. | Food-grade tubing |
| Cut pipe correctly | John Guest pipe cutter for a clean, square cut. | John Guest tube cutter |
| Isolate a section | John Guest shut-off valve for maintenance or repair. | John Guest shut-off valve |
| Adapt to thread | Male, female or swivel elbow BSP/BSPT/NPTF adapters depending on the equipment. | Male BSPT thread adaptor |
| Connect to hose | John Guest pipe-to-hose adapter. | Pipe-to-hose adapter |
| Buy water dispensers | Filtered, chilled, ambient or sparkling water systems. | Water dispensers |
| Study a complete solution | Filtered, chilled or carbonated water for hospitality, offices and public spaces. | AquaTaps solutions |
Not sure which connector you need for your water dispenser?
Send us a photo of the fitting, the outer measurement of the tube and the unit where it is connected. We will help you distinguish 1/4", 3/8", 1/2", 8 mm, 10 mm, 12 mm, 15 mm, BSP, NPTF, hose, filtered water, sparkling water, CO₂, elbow, T, valve, check valve or adapter.
Buy John Guest Check the sizeFrequently asked questions about John Guest connectors for professional filtered and sparkling water
What tube size is most commonly used in professional water dispensers?
The most common size is usually 3/8" OD, especially between filter, chiller, carbonator, dispenser and tap. You’ll also find 1/4", 1/2" and metric sizes such as 8 mm, 10 mm, 12 mm or 15 mm.
What size is used for sparkling water?
It depends on the carbonator, tap, cooler and flow rate. It is common to find 3/8", 10 mm, 8 mm and, in some cases, 1/2" or manufacturer-specific sizes.
Do the same fittings work for water and CO₂?
Not always. Some John Guest ranges may be suitable for potable liquids and inert gases, but you must confirm pressure, tubing, seal, material and application. In sparkling water systems it is not advisable to mix fittings without technical review.
Are 3/8" and 10 mm the same?
No. 3/8" is approximately 9.52 mm. Although it seems close to 10 mm, you should not assume compatibility without checking the tube and the fitting.
Are 1/2" and 12 mm the same?
No. 1/2" outside is approximately equivalent to 12.7 mm, whereas 12 mm is a different metric size. In push-fit, that difference can be critical.
Which John Guest connectors are most useful for HORECA water?
The most common are 3/8" straight connector, 3/8" elbow, 3/8" tee, 3/8" valve, 3/8" check valve, 3/8" to 1/4" reducer, NPTF/BSP adapters, tap connectors, LLDPE tube, clips and tube cutters.
Do I need check valves in carbonated water lines?
In many installations they are advisable or necessary depending on the equipment. They help prevent backflow towards the filter, pump, carbonator or mains. The manufacturer’s diagram and the applicable regulations must be checked.
Can I use John Guest fittings for drinking water for the public?
Yes, as long as you choose the right range for drinking water, dispensing or water treatment and comply with the applicable pressure, temperature, compatibility and hygiene conditions.
Do I need shut-off valves?
Yes, they are highly recommended. They allow you to isolate the filter, chiller, carbonator, tap or dispenser for maintenance without shutting down the entire installation.
Which tubing should I buy for a water dispenser?
It depends on the equipment. Many professional systems use 3/8" OD, but they can also use 1/4", 1/2", 8 mm, 10 mm, 12 mm or 15 mm. Always measure the outside diameter of the existing tube.
Can Install Beer help me identify the fitting?
Yes. As official John Guest distributors in Spain, we can help you identify sizes and connectors if you send us photos, the tube’s outside diameter and details of the equipment it connects to.
Technical note: this guide focuses on professional systems for drinking water, filtration, reverse osmosis, cooling, carbonation and dispensing compatible with push-fit fittings. It must not be used as instruction for fuel gas, aggressive chemicals, heating, critical circuits or non-compatible installations. In premises open to the public, always confirm pressure, temperature, size, thread, hygiene, regulations and product compatibility before installing.