Questions to ask before buying a house with its own private water supply

Buying a house with a Private Water Supply

We strongly recommend that prospective buyers of properties/homes with there own private water supplies read this document. The primary source of this advice is the drinking water inspectorate website.

Key questions

The questions listed at the end of this document are designed to be asked of the owner of the property (through a solicitor or estate agent), or the local authority who regulate private water supplies. Environmental Health Officers are required to establish water quality, the health risks and the future cost liability.

What is a PWS A private water supply?

A PWS is one which is not provided by a water company. About 1% of the population in England and Wales do not have a public supply of mains water to their home and instead rely on a private water supply. Mostly, but not exclusively, these occur in the more remote, rural parts of the country. A  private supply source can be a well, borehole, spring, stream, river or lake and it can also involve storage structures or tanks. Some supplies may serve just a single property or they can be much larger serving many properties and businesses through a network of pipes. Under rare circumstances you may be supplied with mains water by your water company but not receive a bill. In these circumstances you may be receiving a supply through a Private Distribution System.

Single dwelling with its own supply

The regulations do not require a risk assessment If the supply is to a single dwelling and is used only for domestic purposes? The owner can request a risk assessment. In an ideal situation the owner of the supply would have had a risk assessment and monitoring carried out prior to purchasing a property. The risk assessment helps determine the wholesomeness and sufficiency of a supply.

Shared supply

If the supply is shared by two or more properties, then the local authority are required to risk assess the supply and monitor it by sampling at an appropriate frequency.

Risk Assessments

Risk assessments investigate and report on the source of the supply, the surrounding area, water storage tank and treatment, right through to the taps. The aim is to identify any actual or potential contamination. Prospective buyers may also wish to check whether there is any agreement among other property owners as to how these costs are shared or covered. Is remedial action required and how are the costs shared and who is responsible for managing the costs?

Key questions to ask before buying a house with its own private water supply

    • Has a risk assessment already been carried out by the Local Authority, and if so when?
    • Did the local authority advise that improvement works were required?
    • What were the results of any previous sampling by the Local Authority?
    • Did any results indicate a water quality problem? c) Individual premises
    • Are there filters or UV disinfection units installed in the property?
    • Was the equipment installed by a competent installation and Is the treatment appropriate?
    • Is the system compliant with Regulation 5 of the PWS regulations?
    • Is the UV system WRAS approved for use on a drinking water supplies?
    • Has the current owner got any maintenance logs or records for the supply?
    • Are there any compliant spare parts for the supply, including any treatment system?
    • Have there been any problems with the supply such as taste and odour, discolouration or insufficiency.
    • Are there any documented instructions detailing the procedures should any problems with the supply arise, e.g. sufficiency or water quality such as taste or odour issues. These should contain telephone numbers or other contact details to arrange for alternative supplies, pipe repairs, treatment system maintenance etc.
    • Is there a schematic of the supply showing the layout of pipes, tanks, inspection chambers etc. available?
    • Are there schematics or plans for  various parts of the treatment system, stating what each part is, for example any filters, iron or manganese removal systems, and disinfection?

Water testing and report

Springhill Water have been treating private water supplies for nearly 20 years. Contact us on 01422 833121 to arrange a site visit or if you have any questions or would like advice.

Our standard price for testing and a report is £180 plus VAT.

How does UV light disinfection work?

How does UV light disinfection work?

Ultraviolet irradiation

Ultraviolet (UV) irradiation is the preferred method for disinfection of small supplies except

for larger schemes in which it is necessary to maintain a residual disinfectant during storage and

distribution. UV disinfection efficiency is particularly affected by water quality and flow rate. The

water to be disinfected must be of good quality and particularly low in colour and turbidity. It is

generally necessary for the turbidity of water to be less than 5 NTU, preferably much lower, for

successful UV disinfection. Therefore pre-filtration is necessary, especially if Cryptosporidium is

likely to be present, as discussed below.

Aquada UV Disinfection for a private water supply

Aquada UV Disinfection for a private water supply

How does UV light disinfection work?

Special lamps are used to generate UV radiation, and are enclosed in a reaction chamber made

of stainless steel or, less commonly, plastics. Low pressure mercury lamps, which generate 85% of

their energy at a wavelength of 254 nm, are most commonly used; their wavelength is in the

optimum germicidal range of 250 to 265 nm. These lamps are similar in design, construction and

operation to fluorescent tubes except that they are constructed of UV-transparent quartz instead of

phosphor-coated glass. The optimum operating temperature of the lamp is around 40 °C so the lamp

is normally separated from the water by a ‘sleeve’ to prevent cooling by the water. The intensity of

UV radiation emitted decreases with lamp age; typical lamp life is about 10 to 12 months after

which the output is about 70% of that of a new lamp, and lamp replacement is required.

Quartz Sleeve

The usual UV reactor configuration is a quartz-sleeved low pressure mercury lamp in direct

contact with the water; water enters the unit and flows along the annular space between the quartz

sleeve and the wall of the chamber. Other configurations include lamps separated from the water,

for example lamps surrounded by ‘bundles’ of PTFE tubes through which the water flows.

Disinfection will only be effective provided that a sufficient dose of UV is applied. The ‘dose’ of

UV radiation is expressed as an energy flux, in units of mW.s/cm2 (milliwatt seconds per square

centimetre), which is the product of the intensity given out by the lamp and the residence time of

water in the reactor. The minimum dose required for disinfection depends on several factors, including

the susceptibility of micro-organisms but is generally taken to be in the range 16 to 40 mW.s/cm2.

It is important, to ensure effective disinfection, that both residence time and UV intensity are

adequate. UV intensity will be diminished by ageing of the lamp, fouling of the lamp by deposits,

and absorption of UV radiation by water contaminants such as natural colour. For these reasons,

lamps need to be changed at the recommended intervals and the quartz sleeve may require periodic

cleaning. Some units incorporate a manual ‘wiper’ for cleaning whilst others incorporate automatic

mechanical cleaning.

Colour and turbidity

Colour and turbidity will both affect radiation intensity in the reactor and turbidity may protect

micro-organisms from the radiation. The water to be treated should be tested for transmissivity by

the manufacturer or supplier in order to estimate worst-case transmission values and to adjust

contact time accordingly. More advanced units incorporating UV monitors have the facility to

automatically adjust the energy input to the UV lamp to achieve the required UV intensity.

Flow rate

The water flow rate affects the retention time in the reactor, which is designed for a maximum

flow rate. The maximum water flow rate should not be exceeded.


There is evidence that UV is effective in inactivating Cryptosporidium provided that a

sufficient UV dose is applied although there is a dearth of data on effectiveness under high-risk

conditions of water quality. However, where Cryptosporidium is likely to be present and cyst

removal is required then pre-filtration capable of removing particles of 1 mm diameter is

recommended prior to UV disinfection. Pre-filtration provides an additional barrier to passage of

oocysts into the treated water, removes particles that shield micro-organisms from the UV light

and helps to reduce fouling of the UV lamp.


UV irradiation equipment is compact and simple to operate. Maintenance requirements are

modest, although specific systematic maintenance is essential. Other advantages include short

contact time and the absence of any known by-products of significance to health. An ‘overdose’ of

UV presents no danger and actually adds a safety factor. The principal disadvantage is the absence

of any residual effect, necessitating careful attention to hygiene in the storage and distribution


Hard Water Scale

The build-up of scale on the sleeves of the lamps will eventually reduce their transmittance and

they must be cleaned or replaced regularly. Some units have UV intensity monitors and alarms

which provide a continuous check on performance and these are strongly recommended. These

devices may prevent the flow of water if the required intensity of UV radiation is not achieved, for

example when the lamps are warming-up or because of scale formation. UV intensity monitors

may not be available on smaller units and it is therefore essential that the manufacturer’s

instructions regarding lamp warm-up, cleaning and replacement are followed to ensure optimal


Lamp replacement

Lamp replacement is usually a simple operation but may involve a significant downtime for

reactors with many lamps. This difficulty may be overcome by use of multiple units or by having

a treated water storage tank capable of maintaining supply whilst maintenance is carried out. The

materials of construction and design of storage systems should not allow deterioration in water

quality to occur.

Acknowledgement: The primary source of information whilst preparing this document is Drinking Water Regulator in Scotland (DWRS).

Boggy Bit o land

True Springs are rare

True spring supplies are rare in the UK. Even if shown on a map as a spring, the chances are that the water is not coming from deep underground.

Surface derived source

Most ‘springs’ in the UK can best be described as surfaced derived sources. This is because the water probably never passes more than a meter below the surface. The top layers of soil acting a sponge that slowly releases water throughout the year. The water having passed through the top layers of soil, hit shale or rock and then run horizontally. Culverts, land drains, ditches and a under ground pipe channel the water to a collection chamber. Water from the chamber is then piped down to a property, or several properties.

A boggy bit o land

Listen to this short humorous account of what most springs actually are – A bogyy bit o land.

Private water supply spring source protection

Private water supply spring source protection

True Springs are rare

Even when a spring is shown on a map as a spring, the chances are that it is in fact a surfaced derived sources. Springs are rare in the UK as they require a rare type of geology. In the vast majority of cases the water from these ‘springs’ rarely passes more than a meter below the surface. Even in those rare cases where the water rises from deep below ground, the most vulnerable point of contamination is where the water ‘springs’ from the ground and mixes with surface run off, especially after heavy rainfall or a snow melt.
True ‘spring water’ can be of good quality but it must be protected from possible contamination once it has reached ground level. In particular, it is necessary to consider the possibility of pollution from septic tanks or from agricultural activities.

Collection Chamber

A small collection chamber built over the ‘spring’, see Schematic One below, will offer some protection from surface water run-off, but the risk of the water containing pathogens will remain high. This is because water entering the collection chamber is likely to have already been contaminated.
However, building a collection chamber will offer some protection against surface pollution and will provide a small amount storage in periods of high demand and serve as a header tank. The collection chamber should be built so that the water enters through the base or the side. The top of the chamber must be above ground level and it should be fitted with a lockable watertight access cover.

Spring Collection Chamber

Private water supply spring collection chamber

Fenced off area around the Collection Chamber

An overflow must be provided appropriately sized to take the maximum flow of water from the spring. (See schematic Two below). The outlet pipe should be fitted with a strainer and be situated above the floor of the chamber. The chamber should be built of a material that will not impair water quality and be designed to prevent the entry of vermin and debris.
The area of land in the immediate vicinity of the chamber should be fenced off and a small ditch dug up-slope of the chamber to intercept surface run-off.

Take great care when digging around a spring source

We strongly advice that great caution is exercised when digging around a source. Disturbing the top layers of soul, a ditch, or a boulder above or below the point where the water springs to the surface could result in the water taking a new route. In some cases, this can result in the water course being changed permanently.

Fenced off area around a spring

Fenced off area around a private water supply spring collection chamber


Acknowledgement: The primary source of information whilst preparing this document is Drinking Water Regulator in Scotland (DWRS).