Cold water storage tanks

Cold water storage tanks

By on Jul 18, 2016 in Blog |

Cold water storage tanks have various uses; to provide a storage buffer for water against peak demand, storage for basement booster pumps, to provide feed water to calorifiers and to form an airgap break to prevent backflow to the mains supply. However, in our 20 years of checking cold water storage tanks, we have seen some true horrors. Such as these:

Dead birds in water tankPhoto 08-06-2014 02 56 57


Nasty, right???

Before we look at the problems that cold water storage tanks can pose, let us have a look at what we consider to be the characteristics of good quality water.

What do we define as good quality water?

  • Cool temperature 20°C
  • Very low microbiological population
  • Residual chlorine measurable, circa 0.5mg/L
  • Clarity
  • Odourless

What do we define as bad quality water?

  • Warmer temperatures approaching or exceeding 20°C
  • High biological load
  • Visible sediment on the tank floor
  • Corrosion tubercles on bolts or other metalwork
  • Biofilm deposits on the tank surfaces
  • Biofilm on the water surface
  • Scummy deposits at the top water line
  • Reduced free chlorine level compared to incoming water

In the most extreme of cases, there can also be cloudiness to the water, odour and even gas bubbles. With a damp atmosphere in tanks and condensation that appears on the surface above the water level, mould has potential to form. This is also evident through low residual chlorine levels and the presence of mould spores on the outside of tanks. On rare occasions, mould can form within water too.

The design of a tank can also pose a risk to water quality due to:

  • Poor turnover due to excess capacity
  • Poor circulation due to connection positioning
  • Thermal gain due to low performance insulation or a hot situation
  • Corrosion of the tank metalwork due to use of lower grade stainless steel or even mild steel
  • Blistering or break-down of poorly made composite laminates
  • Rough surfaces, nooks and crannies that are ideal for biofilm
  • Water leaks or air leaks allowing ingress of contaminates or vermin

In most new homes the water will be fed directly from town mains, however as some residencies will still have cold water storage tanks, we thought we could answer a few questions you might have surrounding them.


Is stored water safe to drink?

Many older properties have cold water storage tanks in the roof space or loft. In most cases this storage tank will provide cold water to upstairs bathrooms but in some properties all of the cold water taps may be fed from this tank. The condition of this tank may have an impact on water quality. Ideally you should only use a tap connected to the mains water supply for drinking, food preparation or teeth cleaning; however if your drinking water comes from a storage tank then it will be safe to use if the tank is properly designed, correctly installed and kept in good condition.


Do I have a water storage tank?

In older houses the kitchen cold tap maybe the only tap connected directly to the mains if not connected to the water tank. However, in newer homes, especially those with unvented heating systems, all the hot and cold taps are likely to be supplied directly under mains pressure. If you are not sure whether a tap is connected to the mains supply a quick check is to place your thumb over the tap outlet. If you are able to hold back all the water with your thumb when the tap is fully open then the tap is likely to be connected to a tank not the mains. If in doubt you can ask us to help you find out.


Is my tank in good condition?

If you rely on a tank for your drinking water it should meet the following requirements:

  • Not too large, so the water in the tank is frequently replenished with fresh water (250 litres is quite sufficient for most homes)
  • Made of approved materials; traditionally tanks were made of galvanised iron and these rust over time leading to bits in the water or a brown or yellowish tinge or a metallic taste. Nowadays tanks are constructed of plastic (polyethylene) and unlikely to cause problems provided that are designed for drinking water purposes and have a close fitting cover.
  •  Has a lid which excludes light and is tightly fitting and securely fastened, so that birds, vermin, and dust cannot get in to the water.
  •  Has vents, including overflow, that are screened so that insects and particles cannot get in.
  •  Insulated and not exposed to sunlight and not located near to any source of heat so the stored water is kept as cold as possible.
  •  Periodic visual checks to make sure there has not been a build up of scale or deposits on the tank floor and the lid and screens are securely in place.
  •  In public buildings, workplaces, health care premises and social housing all water tanks will be checked and cleaned as part of the arrangements that must be in place for legionella control purposes. If you are renting your property privately then your landlord is responsible for these checks.

Be aware that water in a tank will deteriorate, if:

  •   there is no lid on the storage tank;
  •   the water becomes warm;
  •   too much water is stored and turnover is low;
  •   the tank is made from or lined with an unsuitable material;
  •   work on the tank is carried out by an unqualified person.


If I suspect a problem, who is responsible for putting it right?

The building owner or facilities manager is responsible for all aspects of the plumbing system and its maintenance. New plumbing systems, and alterations and additions to older systems, must comply with regulations known as the Water Fittings Regulations, 1999.

If you are a tenant then your landlord or managing agent should be able to tell you if the drinking water is from storage, what inspection and maintenance has been carried out on the drinking water cistern, and what water quality samples have been taken. A landlord, or managing agent, should also be able to supply records of inspections and sampling results.


What if I suspect the water is unsafe?

You can get in contact with one of our team, and we can give you a full risk assessment to ensure your water systems are safe!


So call us now on 01789 330830 or email and we can give you any further advice you may need, or help you with a risk assessment.


So now you’re clued up on cold water storage tanks, why not get clued up on Legionella? Read our blog here on Legionella FAQ’s!