cold water systems: working principles, positioning, fixing and operation
Cold water systems: working principles, positioning, fixing and operation
Learning objective
Describe how domestic cold water systems deliver clean, wholesome drinking water, and explain the positioning, fixing, connection and operation of key components in direct, indirect, private borehole and boosted systems.
1) Working principle
The aim of any domestic cold water system is simple: provide a continuous supply of clean, cool and potable water to taps and outlets. Achieving that means maintaining water quality, adequate pressure and flow, and protecting the public main from backflow.
2) System types at a glance
- Direct mains fed: all cold outlets are supplied from the incoming main. Hot water may be combi or unvented; the cold side does not use a storage cistern.
- Indirect cistern fed: the kitchen cold (and sometimes a utility or cloakroom tap) is on the main; all other cold outlets are supplied by gravity from a protected cistern in the roof space.
- Private borehole or well: a pump draws water from the source. Systems can be pressure controlled with an accumulator or level controlled by filling a cistern.
- Boosted building systems: where the main cannot meet flow or height, a break cistern and booster set or an approved direct boost arrangement is used.
3) Direct mains fed system
Principle
Every cold outlet connects to the incoming main. Water quality at outlets is controlled at source by the water undertaker; correct backflow protection is still required at fittings and appliances.
Positioning and fixing
- Internal stop valve near point of entry, accessible and labelled.
- Pressure reducing valve where static pressure is high.
- Secure pipework with clips at manufacturer spacings; avoid long unrestrained runs to reduce noise.
Connections and operation
- Use isolation valves at branches to sinks, WCs, appliances and shower mixers.
- Expect pressure to vary at peak demand; select fittings that tolerate variation.
- Where an unvented cylinder or mains pressure heater is installed, ensure the cold feed and control set meet the required flow.
4) Indirect cistern fed system
Principle
The kitchen cold remains on the main; all other cold outlets are supplied from a roof cistern. Lower operating pressure reduces leak damage and can be quieter in use.
Positioning and fixing
- Site the cistern as high as practical to improve head.
- Provide a tight fitting lid, screened warning and overflow pipes, and insulation to sides and lid; protect against frost and undue warming.
- Ensure structural support is adequate for a full cistern.
Connections and operation
- Float operated valve controls the fill; fit service valves for maintenance.
- Distribute from the cistern with a suitably sized trunk, then branch to outlets.
- Maintain hygiene by avoiding dead legs and by flushing during commissioning.
5) Domestic borehole systems
Principle
A pump draws water from a private source. These installations are regulated under the Private Water Supplies Regulations and overseen by the local authority. Regular water quality monitoring is required.
Positioning and fixing
- Locate pumps where access, ventilation and frost protection are adequate.
- Mount on anti vibration bases; secure pipework and cable routes.
- Provide filtration and disinfection equipment, commonly cartridge filters and a UV unit, installed with bypass and isolation for service.
Connections and operation
- Fit non return valves to protect the source and maintain prime where needed.
- Provide pressure gauges and drain points.
- Commission by flushing to clear debris and verifying treatment performance.
6) Borehole with pressure control and accumulator
Principle
A submersible or surface pump charges an accumulator pressure vessel. Pressurised water serves the kitchen cold and may also feed a cistern for other outlets. The vessel smooths demand and reduces pump cycling.
Positioning and fixing
- Site the accumulator upright on a firm base; anchor where required.
- Allow access to the air valve for pre charge checks.
- Fit a pressure switch, gauge, non return valve and isolation either side of the set.
Connections and operation
- Pre charge the vessel to the manufacturer setting before filling.
- Set cut in and cut out pressures to match design flow.
- Provide means to divert flow to the cistern where a mixed arrangement is used.
7) Borehole with level control
Principle
The pump fills a storage cistern. A float switch calls the pump when level is low and stops it when full. All outlets, including the kitchen cold, are supplied from the cistern by gravity or a downstream booster if required.
Positioning and fixing
- As for indirect systems: high cistern position, screened and insulated, with adequate structural support.
- Protect the float switch and cable routing; provide a safe isolation point.
Connections and operation
- Overflow and warning pipes sized and discharged to a visible, safe location.
- Commission by verifying switch operation at low and high levels and by checking refill rates.
8) Boosted systems in taller buildings
Principle
Where the public main cannot meet building height or flow, a booster is used. Directly boosting from the main is generally restricted and often requires consent from the water undertaker. Typical utility thresholds are around 12 litres per minute or 0.2 litres per second for drinking water connections; always consult the undertaker before proposing direct boosting.
Notes on appearance
Boosting can introduce tiny air bubbles and give water a temporary milky look; this aeration clears after standing and is not a deterioration in quality.
Common arrangements
- Direct boosted: with approval, pumps raise water to a high level cistern that then supplies by gravity.
- Direct boosted with small potable header: non drinking services are supplied from a high level cistern; a small 5 to 7 litre header on the boosted line maintains drinking water at the kitchen when pumps are off. Avoid excessive pressure at sinks to minimise splashing and wastage.
- Indirect boosted with break cistern: a break tank is filled from the main and a booster set supplies the building, maintaining a fluid break from the public main. A pressure vessel smooths demand. Lower floors within mains range can remain on the main; upper floors are served by the booster.
Positioning, fixing and connection
- Break cistern at low level with screened vents, lids, warning and overflow pipes; adequate access and drainage.
- Booster set on anti vibration mounts with isolation valves, strainers and non return valves; provide duty standby where required.
- Pressure vessel located adjacent to the set with safe access for checks.
- Fit backflow protection and pressure control appropriate to fluid category and outlet type.
9) Commissioning and operation checklist
- Identify and label the internal stop valve and key isolations.
- Prove backflow devices where fitted; confirm air gaps are unobstructed.
- Record static and dynamic pressure, pump cut in and cut out pressures where applicable.
- Flush and clean strainers; confirm treatment equipment operation on private supplies.
- Test float switches and high level alarms on cisterns; verify overflows discharge correctly.
- Brief the occupier on normal operation and what to do in an emergency.
Cold water systems: working principles, positioning, fixing and operation
Learning objective
Describe how domestic cold water systems deliver clean, wholesome drinking water, and explain the positioning, fixing, connection and operation of key components in direct, indirect, private borehole and boosted systems.
1) Working principle
The aim of any domestic cold water system is simple: provide a continuous supply of clean, cool and potable water to taps and outlets. Achieving that means maintaining water quality, adequate pressure and flow, and protecting the public main from backflow.
2) System types at a glance
- Direct mains fed: all cold outlets are supplied from the incoming main. Hot water may be combi or unvented; the cold side does not use a storage cistern.
- Indirect cistern fed: the kitchen cold (and sometimes a utility or cloakroom tap) is on the main; all other cold outlets are supplied by gravity from a protected cistern in the roof space.
- Private borehole or well: a pump draws water from the source. Systems can be pressure controlled with an accumulator or level controlled by filling a cistern.
- Boosted building systems: where the main cannot meet flow or height, a break cistern and booster set or an approved direct boost arrangement is used.
3) Direct mains fed system
Principle
Every cold outlet connects to the incoming main. Water quality at outlets is controlled at source by the water undertaker; correct backflow protection is still required at fittings and appliances.
Positioning and fixing
- Internal stop valve near point of entry, accessible and labelled.
- Pressure reducing valve where static pressure is high.
- Secure pipework with clips at manufacturer spacings; avoid long unrestrained runs to reduce noise.
Connections and operation
- Use isolation valves at branches to sinks, WCs, appliances and shower mixers.
- Expect pressure to vary at peak demand; select fittings that tolerate variation.
- Where an unvented cylinder or mains pressure heater is installed, ensure the cold feed and control set meet the required flow.
4) Indirect cistern fed system
Principle
The kitchen cold remains on the main; all other cold outlets are supplied from a roof cistern. Lower operating pressure reduces leak damage and can be quieter in use.
Positioning and fixing
- Site the cistern as high as practical to improve head.
- Provide a tight fitting lid, screened warning and overflow pipes, and insulation to sides and lid; protect against frost and undue warming.
- Ensure structural support is adequate for a full cistern.
Connections and operation
- Float operated valve controls the fill; fit service valves for maintenance.
- Distribute from the cistern with a suitably sized trunk, then branch to outlets.
- Maintain hygiene by avoiding dead legs and by flushing during commissioning.
5) Domestic borehole systems
Principle
A pump draws water from a private source. These installations are regulated under the Private Water Supplies Regulations and overseen by the local authority. Regular water quality monitoring is required.
Positioning and fixing
- Locate pumps where access, ventilation and frost protection are adequate.
- Mount on anti vibration bases; secure pipework and cable routes.
- Provide filtration and disinfection equipment, commonly cartridge filters and a UV unit, installed with bypass and isolation for service.
Connections and operation
- Fit non return valves to protect the source and maintain prime where needed.
- Provide pressure gauges and drain points.
- Commission by flushing to clear debris and verifying treatment performance.
6) Borehole with pressure control and accumulator
Principle
A submersible or surface pump charges an accumulator pressure vessel. Pressurised water serves the kitchen cold and may also feed a cistern for other outlets. The vessel smooths demand and reduces pump cycling.
Positioning and fixing
- Site the accumulator upright on a firm base; anchor where required.
- Allow access to the air valve for pre charge checks.
- Fit a pressure switch, gauge, non return valve and isolation either side of the set.
Connections and operation
- Pre charge the vessel to the manufacturer setting before filling.
- Set cut in and cut out pressures to match design flow.
- Provide means to divert flow to the cistern where a mixed arrangement is used.
7) Borehole with level control
Principle
The pump fills a storage cistern. A float switch calls the pump when level is low and stops it when full. All outlets, including the kitchen cold, are supplied from the cistern by gravity or a downstream booster if required.
Positioning and fixing
- As for indirect systems: high cistern position, screened and insulated, with adequate structural support.
- Protect the float switch and cable routing; provide a safe isolation point.
Connections and operation
- Overflow and warning pipes sized and discharged to a visible, safe location.
- Commission by verifying switch operation at low and high levels and by checking refill rates.
8) Boosted systems in taller buildings
Principle
Where the public main cannot meet building height or flow, a booster is used. Directly boosting from the main is generally restricted and often requires consent from the water undertaker. Typical utility thresholds are around 12 litres per minute or 0.2 litres per second for drinking water connections; always consult the undertaker before proposing direct boosting.
Notes on appearance
Boosting can introduce tiny air bubbles and give water a temporary milky look; this aeration clears after standing and is not a deterioration in quality.
Common arrangements
- Direct boosted: with approval, pumps raise water to a high level cistern that then supplies by gravity.
- Direct boosted with small potable header: non drinking services are supplied from a high level cistern; a small 5 to 7 litre header on the boosted line maintains drinking water at the kitchen when pumps are off. Avoid excessive pressure at sinks to minimise splashing and wastage.
- Indirect boosted with break cistern: a break tank is filled from the main and a booster set supplies the building, maintaining a fluid break from the public main. A pressure vessel smooths demand. Lower floors within mains range can remain on the main; upper floors are served by the booster.
Positioning, fixing and connection
- Break cistern at low level with screened vents, lids, warning and overflow pipes; adequate access and drainage.
- Booster set on anti vibration mounts with isolation valves, strainers and non return valves; provide duty standby where required.
- Pressure vessel located adjacent to the set with safe access for checks.
- Fit backflow protection and pressure control appropriate to fluid category and outlet type.
9) Commissioning and operation checklist
- Identify and label the internal stop valve and key isolations.
- Prove backflow devices where fitted; confirm air gaps are unobstructed.
- Record static and dynamic pressure, pump cut in and cut out pressures where applicable.
- Flush and clean strainers; confirm treatment equipment operation on private supplies.
- Test float switches and high level alarms on cisterns; verify overflows discharge correctly.
- Brief the occupier on normal operation and what to do in an emergency.