A temporary drinking water supply on a construction site is a regulated water system, not a hose and a tank. It must satisfy the Water Supply (Water Fittings) Regulations 1999, be designed to BS 8551, be protected against backflow by fluid category, and be managed for Legionella risk.
When is a temporary water supply required?
Any UK construction site where permanent mains water is not yet available — or where the permanent supply is insufficient for construction activities — needs a temporary supply. That covers new-build developments before mains connection; refurbishment where the existing supply is isolated; remote infrastructure projects on roads, railways and pipelines; and demolition or remediation sites where the original supply has been decommissioned.
The supply serves two distinct needs, and conflating them is the single most common failure on site:
- Drinking water (wholesome water) — for hand-washing, welfare facilities and drinking. Must meet Water Supply (Water Quality) Regulations 2016 standards.
- Process water — for dust suppression, concrete mixing, tool washing and site cleaning. Need not be wholesome, but must not create environmental or safety risks.
This guide addresses the drinking water supply. Process water is covered in our guides to construction dewatering and surface water management.
The Water Supply (Water Fittings) Regulations 1999
The Water Supply (Water Fittings) Regulations 1999, and the parallel Scottish Water Byelaws 2004, govern any connection to a public water supply. They are enforced by water undertakers and their appointed water regulation advisers.
| Requirement | Regulation | Practical implication |
|---|---|---|
| Notification | Reg 5 | Notify the undertaker before connecting a temporary supply |
| Backflow prevention | Reg 6 | Protection appropriate to the fluid category |
| Materials | Reg 7 | WRAS-approved materials only |
| Water fittings | Reg 8 | Fittings of an appropriate standard that do not cause waste |
| Prevention of contamination | Reg 3 | System must not impair water quality or prejudice public health |
Under Regulation 5, the undertaker must be notified of any temporary supply pipe above 12 mm diameter, any tank, cistern or booster pump, and any backflow prevention device. Failure to notify is a criminal offence and can result in disconnection.
Fluid categories and backflow protection
| Category | Description | Example on site | Minimum protection |
|---|---|---|---|
| 1 | Wholesome water | Mains supply | None required |
| 2 | Aesthetic quality altered | Heated or softened water | Tap gap or single check valve |
| 3 | Slight health hazard | Water with additives such as glycol or dye | Break tank with air gap |
| 4 | Significant health hazard | Toxic chemicals, pesticides | Verifiable backflow preventer (RPZ) or air gap |
| 5 | Serious health hazard | Human waste, pathogens | Type AA air gap only |
Category 4 is common on construction sites: water used for concrete mixing, chemical dosing or tool washing that could contain cement, oils or solvents. Any connection between the drinking water supply and a Category 4 use requires a verifiable backflow preventer or a physical air gap.
BS 8551: design and operation
BS 8551 is the British Standard for temporary water supplies. It is not statutory, but it is referenced by the Water Fittings Regulations and forms the benchmark for what counts as an appropriate standard. It requires that temporary systems are designed for the site population, protected from contamination, maintained and inspected at least weekly, and documented with drawings, maintenance records and water quality results.
Peak demand
Peak instantaneous demand determines pipe sizing and storage volume: Q_peak = N × q × F_peak, where N is the number of people on site, q is per-capita demand (BS 8551 suggests 35 L/person/day for construction welfare) and F_peak is the peak factor, around 3.0 for the morning-break, lunch and end-of-shift peaks.
- Average daily demand: 50 × 35 = 1,750 L/day.
- Peak flow over an 8-hour shift: 1,750 × 3.0 / (8 × 3,600) ≈ 0.18 L/s.
- Hydraulic pipe size at 2 m/s: d = √(4Q / πv) ≈ 11 mm.
- Practical minimum: BS 8551 requires at least 15 mm; use 22 mm MDPE to hold pressure and resist blockage.
Storage tank sizing
Where the supply relies on mains top-up, storage must cover 24 hours of demand plus any fire reserve. For the 50-person site: 1.75 m³ for 24 hours, plus 5,000 L if a 30-minute hose run is needed with no hydrant, giving about 6.75 m³.
Tanks must be WRAS-approved for potable contact, opaque or covered to prevent algal growth, vented through insect-proof mesh, and either elevated to give at least 2 m static head or served by a booster pump.
- Static head: 5 − 2 = 3 m.
- Friction head: at Q = 0.18 L/s, v ≈ 0.47 m/s and Re ≈ 10,000; with f ≈ 0.03, hf = f (L/D)(v²/2g) ≈ 0.77 m.
- Residual pressure at the tap: 10 m (1 bar).
- Total dynamic head: 3 + 0.77 + 10 ≈ 13.8 m.
- Duty: 0.18 L/s at 14 m — a 0.25 kW variable-speed booster with a 50 L pressure vessel to limit cycling.
Backflow prevention and cross-connection control
Backflow on construction sites occurs by five mechanisms: back-siphonage, where negative mains pressure draws fluid from a lower container — classically a hose left submerged in a bucket; back-pressure, where downstream pressure from a booster or elevated tank exceeds mains pressure; cross-connection, a physical link between wholesome and non-wholesome systems; submerged outlets, where a tap or hose discharges below the water level in a vessel; and shared fittings, a single tap used for both drinking and chemical mixing.
| Protection | Application | Relative cost |
|---|---|---|
| Type AA air gap | Category 5 (serious hazard) | Low — a physical disconnect |
| Verifiable backflow preventer (RPZ) | Category 4 (significant hazard) | High |
| Double check valve | Category 3 (slight hazard) | Medium |
| Single check valve | Category 2 (aesthetic) | Low |
| Terminal tap gap | Category 1–2 | Very low — a design feature |
The cheapest and most reliable solution on a construction site is not a valve at all: it is physical separation — two entirely independent systems sharing no pipes, taps or hoses.
Hose management
Hoses are the highest-risk component of any temporary supply. Colour-code them (blue for drinking, yellow for process, red for firefighting); store them coiled on a reel, off the ground and capped when not in use; never leave one submerged in a tank, bucket or puddle; and inspect daily for damage, contamination or unauthorised use.
Water quality monitoring and Legionella control
| Parameter | Standard | Frequency |
|---|---|---|
| E. coli | 0 per 100 mL | Weekly |
| Coliforms | 0 per 100 mL | Weekly |
| Turbidity | <1 NTU | Daily (in-line) |
| pH | 6.5 – 9.5 | Daily |
| Free chlorine | 0.2 – 0.5 mg/L if dosed | Daily |
| Lead | <10 µg/L | Monthly if pipework is new |
| Copper | <2 mg/L | Monthly if pipework is new |
A construction site is not domestic premises, so the Water Quality Regulations do not bite directly. But the Health and Safety at Work etc. Act 1974 and the Workplace (Health, Safety and Welfare) Regulations 1992 require employers to provide wholesome drinking water — and the Water Quality Regulations are the de facto standard for what wholesome means.
Legionella risk
Legionella pneumophila grows in warm, stagnant water between 20 and 45°C where biofilm and sediment are present. Construction water systems are high-risk on every count: tanks sit in the sun, use is intermittent across weekends and holidays, dead legs are common in temporary pipework, and biofilm forms quickly in new plastic pipe.
Control means keeping cold water below 20°C by insulating and shading tanks; designing for daily turnover so that a tank larger than twice daily demand is treated as too large; shock chlorinating monthly or after any modification; cleaning and disinfecting tanks quarterly; removing dead legs longer than twice the pipe diameter; and dismantling and descaling showerheads and taps monthly.
- Solar heat gain: 500 × 5.5 = 2,750 W.
- Convective loss at h = 10 W/m²·K and ΔT = 5 K: 275 W.
- Net gain: 2,475 W.
- Rate of rise: 2,475 / (2,000 × 4,180) ≈ 1.07 K/h.
The tank goes from 15°C mains temperature to above 20°C in under five hours of sun. Paint it white, jacket it, or move it into shade — white paint alone cuts solar gain by roughly 85%.
Chlorination of non-mains supplies
If the supply comes from a borehole, spring or rainwater rather than the mains, disinfection is mandatory. Dose = demand + residual, where demand is typically 1–5 mg/L for groundwater and 5–20 mg/L for surface water, and the target free residual is 0.2–0.5 mg/L at the tap after 30 minutes contact. The chemistry and contact-time design are covered in chlorination and disinfection, with UV disinfection as the no-chemical alternative and pH correction where the source is aggressive.
- Dose: 3.0 + 0.3 = 3.3 mg/L.
- Mass rate: 2,000 L/h × 3.3 mg/L = 6.6 g/h.
- As 10% sodium hypochlorite: 66 g/h, roughly 0.1 L/h, injected into the rising main through a static mixer.
- Contact tank: 1 m³ gives 30 minutes at 2 m³/h.
Safety: store hypochlorite in a bunded, ventilated, locked store with spill kits and eye wash. Never mix it with acid — that releases chlorine gas.
Frequently asked questions
Can I use a garden hose for drinking water on a construction site?
No. Garden hoses are not WRAS-approved for potable contact. They contain plasticisers and stabilisers that leach into water, especially in sun, and they cannot be cleaned internally so they harbour biofilm. Use WRAS-approved MDPE or barrier pipe with approved fittings.
How often must I test temporary drinking water for bacteria?
Weekly for E. coli and coliforms during active use. A direct mains connection with no storage may justify monthly testing, since the undertaker already tests the mains. Any borehole, tank or non-mains source needs weekly testing. Send samples to a UKAS-accredited laboratory within 24 hours, refrigerated below 10°C.
Do I need a licence to abstract water for a temporary supply?
Abstraction above 20 m³/day from surface water or groundwater needs a licence from the Environment Agency under the Water Resources Act 1991. Drinking water alone rarely reaches that — 50 workers at 35 L is 1,750 L/day — but process water for dust suppression and concrete mixing often does. Aggregate all abstractions, including dewatering, when checking the threshold.
What is the minimum welfare water requirement per worker?
The Workplace (Health, Safety and Welfare) Regulations 1992 require an adequate supply of wholesome drinking water, readily accessible and sufficient for the number of people. BS 8551 uses 35 L/person/day as a design figure, but the legal test is sufficiency — a site in summer needs more than the same site in winter. Treat 3.5 L/person/shift as an absolute floor for drinking alone.
Can I use rainwater harvesting for construction site drinking water?
Only with full treatment — filtration, UV and chlorination. Rainwater is not wholesome: it collects atmospheric pollutants, bird droppings and roof contaminants. On a temporary site it is rarely cost-effective for drinking; use it for process water instead. If you do use it for drinking, it must meet the Water Quality Regulations and you should consult the local environmental health officer.
What happens if my temporary supply fails a water quality test?
Stop use immediately and provide bottled water. Investigate for cross-connections, tank contamination, dead legs or source problems. Shock chlorinate, hold, and flush. Re-sample after 24 hours of normal use. If E. coli is present, notify the local authority environmental health officer and the water undertaker. Record the failure, the actions taken and the re-test results in the site water safety log.