Cold Water Tanks

Cold water tanks (sometimes called header tanks) are storage containers (tanks) which hold water. They can be used in both domestic and commercial settings. They are often situated in lofts or attics, which means the pressure of gravity can be used to feed taps, toilets, showers, baths, heating systems, etc. The water tank is fed from the water mains and maintains a constant water level using a float valve. Various sizes of tanks are available; a size should be chosen to meet the maximum peak demand of the property. It is rare to see cold water tanks in new builds, as they have been replaced with newer technologies, such as combi boilers.

Most cold water tanks are black (to limit light and algae growth) and made from plastic (although other materials are available). They can act as a backup supply when there are water outages or when pressure drops. Cold water storage tanks are often insulated to manage the water temperature and particularly to protect against water freezing. An overflow pipe helps to protect against flooding where the ballcock fails.

Essential qualities to look for in cold water storage tanks

Look for qualities like these when you buy cold water storage tanks:

• Bacteria protection - the smooth internal surface prevents biofilm build-up and the development of bacteria such as Legionella

• Capacity - a range of tank sizes is available; a plumber can advise on the tank size you need based on your peak demand

• Durability - the tank will be made with a high-grade material such as MDPE, stainless steel, or GRP. This ensures long-term use and the ability to withstand pressure without cracking, leaking and gradual degradation

• Ease of cleaning - a dedicated drain outlet at the water tank base eases cleaning, emptying and maintenance

• Insulation - available in premium models, pre-insulated tanks regulate water temperature. They prevent water from freezing in winter, and prevent it from warming up during the summer months

• Overflow management - there are in-built overflow systems to prevent excess water from discharging outside the tank

• Security and tamper-proofing - to protect from children, rodents, insects, dust and light, etc. There needs to be security and tamper-proofing features. Look for a well-fitted sealed lid and a cover, which prevents contamination and unauthorised access

• UV-resistance - look to buy UV-resistant tanks; this plastic type will be less brittle when exposed to UV rays from sunlight

• Water quality protection – look for WRAS approval, which ensures the tank meets strict UK water safety and quality regulations. The WRAS accreditation will also prove that the water tank is potable and intended for human consumption

How much does a new cold water tank cost?

The cost varies depending on several factors. These prices are for the tank purchase only and do not include installation or VAT:

• Small domestic tanks (100–250 litres) - £40 to £100

• Medium tanks (300–500 litres) - £90 to £180

• Large domestic tanks (500–1,000 litres) - £150 to £350

• Commercial or high‑capacity tanks (1,000 litres+) - £350 to £800+

Criteria that affect cost:

• Brand and quality

• Delivery charges

• Included fittings and accessories (or not)

• Insulation (or not)

• Material type

• Shape and design

• Size and capacity

FAQs

1. Is it normal to use loft water tanks?

Yes, it can be considered "normal" to use cold water loft tanks. This is decreasing over the years, though, due to the advent of modern alternatives such as direct mains water supply plumbing systems, unvented cylinders, or combi boilers, which remove the need for a loft tank.

Loft water tanks can be considered "traditional" as they are a feature in the lofts or attics of many older homes. They feed mains pressure to bathrooms, especially for hot water cylinders (gravity-fed systems).

2. How durable are cold water tanks?

All tanks can be considered durable, but their lifespan will vary based on criteria such as material, build quality, installation quality and effective maintenance:

• Plastic (various types, e.g. polyethylene) - between 10-25 years. They are rust and corrosion-resistant, lightweight and low-maintenance, but need to be UV-stabilised

• Galvanised steel - between 15-23 years. Effective, but prone to rusting if the protective coating becomes damaged, interior linings (particularly after 20 years) can protect against this

• Stainless steel - 25+ years and a high-quality option. More expensive initially, but corrosion-resistant

• GRP (Glass-Reinforced Plastic) - 15-25 years, an increasingly popular and cost-effective option, which often requires less maintenance than steel alternatives

• Other options - although less popular, copper and concrete water tanks can also be found

3. Are they known as header tanks in the UK?

Yes, cold water storage tanks are interchangeably called "header tanks". There is no difference; it is just personal preference. The word "header" originates from its high/elevated water supply (often in lofts). This is, of course, a generalisation, as some tanks are found in airing cupboards or enclosed cupboards, etc.

4. Why are cold water tanks usually black?

Most existing tanks in heating systems are indeed black or dark grey, but this is not for aesthetic reasons. It is more because of the qualities of black, which blocks light from entering the tank. Black and dark colours prevent algae growth and bacterial development, which helps with long-term water storage.

Of course, loft tanks are out of sight too, so when manufactured, low emphasis is placed on offering a variety of appealing colours. Although Plumbing World do not sell them, there are lighter coloured water tank products on the market (e.g. food and beverage processing, where tanks are colour-coded), but these tend to be for specialist applications rather than standard domestic use.

5. Are cold water tanks easy to maintain?

Yes, existing tanks are generally easy to maintain. Routine visual checks are needed, such as checking that the lid is secure, that insulation is intact, that debris is cleared, and there are no obvious adverse signs (e.g. discolouration). Simple maintenance, such as cleaning the ball valve and overflow occasionally, is all that is needed regularly.

6. Are smaller models available where there is limited space?

Yes, smaller cold water tank models can be bought. Often used in lofts, airing cupboards, or tight spaces, typical dimensions might be:

• 18”x18”x12” – storing 18 litres – see: Cold Water Expansion Tank 18 x 12 x 12 Inches

• 20”x15”x18” – storing 55 litres – see: Cold Water Poly Tank 20 x 15 x 18 Inches

• 24”x24”x12” – storing 90 to 150 litres – see: Cold Water Poly Tank 24 x 12 x 24 Inches

Exact dimensions and capacities will vary by manufacturer and the tank shape, so always check product specifications.