Water Composition

How to find out about the composition of your tap water – public water supplies
A consumer may request information from their water supplier about their water supply. The supplier must provide information about the consumer’s supply free of charge and within seven days. Where the request relates to information outside the consumer’s supply zone, a reasonable fee may be charged for provision of the information.

Most water suppliers provide this information online and Water UK publishes a listing of website addresses for all water suppliers in England and Wales as well as the Island Water Authorities (Guernsey Water, Jersey Water, Council of the Isles of Scilly & Isle of Man). In Scotland, the Drinking Water Quality Regulator for Scotland provides information on drinking water quality while in Northern Ireland, Northern Ireland Water provides that information. Many suppliers offer a postcode based search facility allowing online access to data. Some provide the information online at the supply zone level and it is necessary for the consumer to find out in which supply zone their premises are located. A few suppliers will only provide information about drinking water quality in response to an E-mail or letter.

How to find out about the composition of your tap water – private water supplies
Local authorities maintain comprehensive records about the private water supplies in their areas. Where a consumer receives water from a private water supply, it will be necessary to contact the local authority to find out what analysis data is available.

Why information about the composition of water might be required
Consumers may need detailed information on the quality and composition of water supplied to their own premises for a number of reasons:

Water heaters and combination boilers
Hard water causes the build up of scale in kettles, washing machines, boilers and hot water systems. The deposition of scale can damage heating elements and make the heating process less efficient. For this reason, Government guidance given in the Domestic Heating Compliance Guide requires that “where the mains water hardness exceeds 200 parts per million (as CaCO3), provisions should be made to treat the feed water to water heaters and the hot water circuit of combination boilers to reduce the rate of accumulation of lime scale”.

Softening and water conditioning equipment
Information about the hardness of drinking water is important when deciding whether to install water softening or water conditioning equipment. Hard water increases the quantity of soap, washing up liquid and washing powders required for washing and cleaning and also causes staining and deposits on sanitary ware. There is also anecdotal evidence that softened water can reduce skin irritation although a research study at Nottingham University to investigate whether water softeners help reduce the severity of eczema showed no objective difference in outcomes between the children whose homes were fitted with a water softener and those without.

Maps showing hardness levels in water supplies throughout the UK are available but some water hardness maps provide insufficient detail and pockets of relatively soft water are found within regions shown as hard water areas. A more detailed map can be viewed on the DWI website in the Water Hardness Advice Leaflet but the scale is too small to allow precise location of premises near boundaries of hard/soft water areas. . For this reason you should ask your water supplier for information specific to your premises. 

Water softening equipment should be installed in accordance with WRAS Guidance IGN 9-07-01, which specifies, among other things that a separate supply of un-softened water should be provided for potable purposes.

Corrosion of household water supply systems – public water supplies
Chemical, physical and biological characteristics of water can influence corrosion of pipes and fittings. The regulatory requirement on water suppliers to reduce contamination from pipes has resulted in public water supplies that are not unduly corrosive towards metals and alloys used in water supply systems. Nevertheless some public water supplies may cause dezincification of brass fittings (See also WSAA84). In these cases the specification of dezincification resistant fittings is important when installing or re-furbishing water supply systems. Other more complex factors can cause accelerated corrosion of copper pipes and this subject is addressed in the FWR ROCK “Causes of Copper Corrosion in Plumbing Systems” which is available on this website.

Corrosion of household water supply systems – private water supplies

The absence, or inadequacy, of suitable treatment results in many private supplies being corrosive towards the metals and alloys used in water supply systems. The greatest concern will be the risk to health from lead and other toxic metals, but corrosion of pipes and fittings, discolouration of laundry and sanitary ware and taste complaints are all associated with corrosive attack on plumbing systems. Information about water composition and implications for corrosion control is given in the “Manual on Treatment for Small Water Supply Systems”, which can be accessed on the DWI website.. A more detailed description of how the chemical composition of water affects its corrosion potential is available on the Wilkes University website

Water use in home brewing
Where tap water is water is to be used in brewing, the concentration of some inorganic salts, as well as the pH and alkalinity of the water can have a significant effect on the fermentation process. For more information.

Water use in aquaria
Where an aquarium or fishpond is filled or topped up with tap water the hardness, pH, alkalinity and the nitrate and ammonium ion levels will be of interest. For more information. Note that water used in ponds and aquaria must be de-chlorinated in order to avoid fish mortalities.