Most households in the UK are supplied by water from a public water utility company such as United Utilities, Yorkshire Water etc.. A private water supply is a supply NOT provided by one of these companies.
Water in a private water supply comes from a borehole, spring, well, stream or lake. Most water that comes from a source other than a borehole is properly called a “surface derived” source. For example, sometimes what appears to be a spring is really the outlet for field drains. In other cases shallow wells are really getting water from just below the soil surface and so can easily be contaminated.
Some springs will have their source deep under ground but they will be vulnerable to the ingress of surface water and therefore they would also be classified as a surface derived source. In the UK, springs that are not vulnerable to the ingress of surface water are very rare.
All surface derived sources (including most springs) will normally require some form of water treatment before they would be suitable for use in the home or as part of a production process.
Borehole water is less vulnerable to the ingress of “fresh” surface water, reducing the risk of contamination. However, approximately 50% of all boreholes fail to meet microbiological standards at some point through the year. In addition, many boreholes contain naturally occurring contaminants such as iron, manganese or “hardness” that will stain clothes, fixtures, fittings and sanitary ware or will make the water unpleasant to drink.
The risk of a borehole containing pathogens such as E.coli, Coliforms, Cryptosporidium and Giardia at some time during the year is moderate to high. It is therefore advisable to disinfect a borehole supply. The disinfection system of choice for most owners of private water supplies in the UK is Ultra Violet disinfection.