A cold water storage tank in a loft must have a cover. In England and Wales, Schedule 2 of the Water Supply (Water Fittings) Regulations 1999 requires a storage cistern to be fitted with a cover that keeps out light and insects, an overflow pipe that insects cannot enter, and insulation. A missing lid, or debris floating in the water, means the tank no longer meets that standard. Fitting a cover, screening an overflow or cleaning the tank is work for a qualified person. You can look, and you can report what you see.
Does a loft water tank need a lid? What Schedule 2 of the Water Fittings Regulations says
A loft cold water storage cistern needs a cover under the Water Supply (Water Fittings) Regulations 1999, which apply in England and Wales. A storage cistern is simply a tank that holds water for later use. Schedule 2 requires every storage cistern to be installed so the risk of contaminating the stored water is minimised. The purpose of the Regulations is to prevent contamination and waste of water supplied by a water undertaker.
- A cover, fitted so that light and insects are excluded from the stored water.
- An overflow pipe with a suitable warning of an impending overflow, made so insects cannot get in.
- Insulation against freezing and against undue warming of the stored water.
- Cold water pipework arranged so the water is not warmed above 25°C, so far as is reasonably practicable.
Building Regulations in England sit alongside this. Approved Document G states that water supplied through an installation complying with the Water Supply (Water Fittings) Regulations 1999 may be assumed to be wholesome. It also expects the cold water storage cistern to stand on a flat, level, rigid platform that supports the filled tank and extends at least 150 mm beyond its sides. Scotland and Northern Ireland have their own equivalents, so the wording above applies to England and Wales only.
Is an uncovered loft tank an offence, and is a pre-1999 tank exempt?
A water fitting lawfully installed before 1 July 1999 falls outside the Water Supply (Water Fittings) Regulations 1999, but an old loft tank without a lid is not automatically safe in law. Section 73 of the Water Industry Act 1991 makes it an offence for an owner or occupier to intentionally or negligently cause or permit a fitting they are responsible for to be out of repair, so that water is or can be contaminated, wasted, misused or unduly consumed. On summary conviction the penalty is a fine up to level 3 on the standard scale.
The duty attaches to the condition of the fitting, not to the date it went in. An uncovered loft cistern with debris in it is therefore a repair question, not a grandfather-rights question. Whether replacing or altering a cistern has to be notified to your water undertaker beforehand is set by Regulation 5 of the 1999 Regulations. Your installer checks that point against the Regulation before any work starts.
Debris, insects or sediment in a loft tank: what it means and what you may safely do
Debris in a loft cistern points to a missing or badly fitting cover, or to an overflow or vent that is not screened. The Drinking Water Inspectorate says the cover should exclude light, fit tightly and be fixed securely, so birds, vermin and dust cannot reach the water. Vents, including the overflow, should be screened so insects and particles cannot get in. There should be no layer of scale or sediment on the bottom of the tank.
- No cover on the cistern.
- The stored water becoming warm.
- Too much water stored for the amount used, so turnover is low.
- A tank made of, or lined with, unsuitable material.
- Work on the tank carried out by an unqualified person.
Do not reach into a loft cistern and do not drink from it to judge the water. Fitting a cover, screening an overflow, cleaning or disinfecting a cistern is work for a qualified person — the Drinking Water Inspectorate lists work by an unqualified person among the reasons stored water deteriorates. Looking at the tank and reporting what you saw is the safe step. Where water is stored for drinking, the Inspectorate advises an annual check of the condition of the tank and the water quality.
Why the temperature of a loft tank matters: HSE guidance on legionella and cold water storage
Legionella bacteria multiply in water between 20°C and 45°C, stay dormant below 20°C and do not survive above 60°C, according to HSE. Cold water should therefore be stored and distributed below 20°C. A loft tank sitting under a hot roof in summer is the classic place where that limit slips. HSE's control measures for cold water tanks are a tight-fitting lid, insect screens, periodic cleaning, keeping the stored volume no larger than needed, and keeping the tank cool and insulated.
Landlords carry a duty to assess the risk of exposure to legionella under health and safety law, which covers England, Wales and Scotland. HSE is clear that a detailed assessment is not needed for most rented homes and that there is no legal requirement for a legionella test certificate. Ordinary homes are generally low risk because water is used and replaced regularly. HSE gives systems with no stored water at all as an example of low risk.
The two tanks in a loft: cold water storage cistern or feed and expansion tank?
Many lofts hold two tanks, and the rules are not the same for both. The large one stores drinking-quality water for taps and the cylinder; the small one belongs to the heating circuit.
| Criterion | Cold water storage cistern (the large tank) | Feed and expansion tank (the small tank) |
|---|---|---|
| What it supplies | Cold water to taps and bath, and usually the hot water cylinder | Keeps the heating circuit topped up and takes up expansion of the heated water |
| Water inside it | Mains water that reaches taps you wash and drink from | Heating water that circulates through radiators and boiler, never drunk |
| Which rules apply | Water Supply (Water Fittings) Regulations 1999, Schedule 2: cover, screened overflow, insulation | Manufacturer instructions and BS 7593 on treating water in central heating systems |
| What dirt in it means | Contamination risk for water used for washing and drinking | Sludge that can damage the appliance and reduce efficiency |
| Where it sits | Lower and larger, with a float valve on the mains feed | Smaller, normally set higher than the large tank |
Both tanks belong to an open-vented system, the type served by a regular or heat-only boiler. Water appearing in the large tank from the vent pipe is a separate symptom with its own causes — see water coming out of the vent pipe into a loft tank. If you are unsure which tank you are looking at, say what you saw and where it sits when you call an engineer.
Can the loft tank be removed instead of repaired?
Removing the loft cold water cistern is possible if the hot and cold system is changed to run off the mains. With an unvented cylinder, no cold water storage cistern is needed in the building, because water comes straight from the mains rather than from the loft tank. That also takes away the frost risk a tank carries in an unheated loft. The cylinder work is not a DIY job: an unvented cylinder may only be installed by a person qualified for G3 work.
Whether that change suits your home depends on the mains flow and pressure and on where a cylinder could stand. Our guides on whether you still need the cold water tank in the loft and on converting a vented system to an unvented cylinder set out what changes in the house. You can arrange a free home survey and get a written fixed price before anything is agreed. If you would rather lose the loft tank than keep patching it, see Megaflo and unvented cylinders.
Sources
- The Water Supply (Water Fittings) Regulations 1999, Schedule 2
- The Water Supply (Water Fittings) Regulations 1999 (as made)
- Water Industry Act 1991, section 73
- Drinking Water Inspectorate: Water Storage Tanks and Cisterns
- HSE: Hot and cold water systems (legionella control)
- HSE: Legionella and landlords' responsibilities
- Approved Document G with 2024 amendments
- Heatrae Sadia: how does an unvented cylinder work