Private Water Supplies

What is a Private Water Supply? (PWS)

PWS are generally defined as supplies which are not provided by a water supply company. They can supply one to several hundred dwellings. Many domestic, industrial, commercial and hospital sites have their own supplies that can provide water at a much lower cost than the ‘mains’.

Water Sources and Quality

Water is abstracted from rivers, streams, lakes and reservoirs (in Scotland burns and lochs as well). These sources are called surface supplies. Water drawn from wells, boreholes and springs are normally classed as groundwaters.

Surface waters may originate from groundwaters, surface run off and combinations of both. These waters are rarely fit to drink (potable) due to pollution by microbiological, industrial and agricultural contaminants without appropriate treatment.

Groundwaters are generally of far higher quality and often perfectly safe to drink without any treatment. These waters are less susceptible to accidental pollution but can be difficult to treat if they become contaminated.

There are several types of groundwater but those emanating from ‘confined aquifers’ which are usually the deeper sources are the purest from a microbiological aspect. Groundwater which is not confined is ‘free’ and is fed from seepage which may be via fissures or porous strata communicating with the ground surface.

The shorter the time the water spends travelling to the aquifer the greater the risk of microbiological contamination. Both water levels and quality are likely to vary more rapidly than those in confined aquifers.

Another type of groundwater is ‘Alluvial’ which is found in the sands and gravels adjacent to rivers. These waters are likely to reflect the contaminants in the river water but the alluvial material will usually act as an excellent mechanical filter. The chemical qualities of the water can also be improved in some locations.

Sourcing the Water and Avoiding Problems

It is not uncommon to find that excellent quality sources of water are adversely affected by contaminated water gaining access due to defective abstraction methods or poor maintenance.


One of the most common sources prone to these problems are springs but with careful development and protection, good quality water can often be obtained. It is important to ensure that a spring originates from a carefully protected aquifer (preferably confined). There are situations where an apparent spring is the discharge from a network of pipes buried just below ground level. These sources are little or no better than surface waters.


Wells usually tap into fairly high aquifers and are shafts dug into the ground either mechanically or by hand. Some are brick lined and sometimes dug through solid rock but nowadays they are usually constructed with concrete ring segments. High aquifers are more likely to suffer from microbiological contamination than deeper ones. It is also usual to find heavy contamination caused by the ingress of surface water through inappropriate, poorly fitting or missing well covers. Seepage of water can also occur through defective brickwork or seals between well segments. Appropriate construction and maintenance can provide an acceptable source of water in some situations.


Boreholes are drilled using rotary or percussive drilling. The smallest bores normally have an internal diameter of approximately 4″. In England and Wales these are referred to as 4″ bores but in Scotland the size usually refers to the size of the hole drilled rather than the final diameter e.g. a finished internal diameter of 4″ will usually be called a 6″ bore! This can cause confusion when specifying pumps.

There is a tendency by some borehole drillers to tap as many water bearing strata as possible in order to maximise the water yield. During periods of high rain fall water demand is usually at its lowest but the higher strata’s will be producing at their maximum rate. During dry spells when demand is high the higher strata dry out!

The quality of the bore water is adversely affected by this practice due to the intermingling of the differing waters. Those that have spent insufficient time for the natural purification processes to take place will contaminate the deeper and probably purer waters. These are likely to be anaerobic (devoid of oxygen) and if they contain dissolved metals, especially iron, these can react and cause severe obstructions to pumps and pipe work. In these situations it is common to find that removal and cleaning of the bore pump has to be carried out every few months.

Some borehole drillers give clients the choice of whether or not to use only the deeper aquifer(s). Preventing higher level ingress does cost more in areas where specialised techniques have to be employed but if the risks are not fully appreciated failure to do this can be an expensive mistake.

One of the most common causes of microbial contamination in boreholes is the ingress of surface and high level waters. Often the top of the borehole is in a chamber below ground level which can accumulate water. If the top of the bore is not fitted with a waterproof cap the water in the chamber simply runs down the bore. Even when the risk of surface water ingress is virtually impossible it is common practice to leave bores open. The remains of small animals have been found when pumps are lifted.

A carefully constructed borehole, drawing its water from a confined aquifer and equipped with correctly installed head works will inherently provide the purest water from a microbiological point of view.

The mineral content of the water will depend on the type of the rocks and soil that the water comes into contact with. If there is appreciable limestone or chalk the water will normally be hard and alkaline in nature. Granite’s and sandstone’s tend to yield soft and acidic water with low levels of minerals.

Some waters are high in Iron (Fe), Manganese (Mn), Aluminium (Al), Fluoride (F) and Arsenic (As), (not an exhaustive list!). In spite of these apparent disadvantages the chemical makeup of the water tends to be reasonably consistent which simplifies treatment and allows equipment to operate with the minimum of attention.


Your local authority (LA) is responsible for monitoring, risk assessing and recording all PWS’s in their district, however this is a massive task for them to undertake. Usually underfunded but not lacking in enthusiasm they are a good place to start if you have recently moved into a property with a PWS. PWS’s are usually part of the Environmental Health Team’s portfolio.

The DWI (Drinking Water Inspectorate) advises the LA’s and ensures that the regulations are enforced. The LA’s have to submit an annual PWS report to the DWI.

Responsibility for a PWS is that of the ‘relevant person’. In most cases this is straight forward with the owner/occupier being the relevant person. In other cases it can be very ambiguous as to who is relevant. Sites with multiple users or boreholes located on adjacent properties can make selecting the appropriate person difficult.

Most of the time unofficial agreements between users run along well but in other cases it can become very messy! You could be the ‘relevant person’ so get to know your private water supply!

PWS’s using less than 10m3/day (10,000 litres per day) of water are very much as the old class F supply. These serve an owner/occupier single domestic property. Generally you are unlikely to receive a visit from your LA unless you approach them for help.

Once a PWS is used for anything commercial it must be compliant and safe. This could be as small as a B & B or a stand pipe to a small camp site, anything that involves a member of the public or someone not associated with the original users of the supply using the water.

Then there are larger commercial sites such as hotels, garden centres, breweries, distilleries and restaurants etc. Depending on how much water they use will determine how often they are monitored by the LA.

Industrial supplies are also required to be compliant and again monitored by the Local Authorities.

Interpretation of the regulations can vary a little between LA’s. This is most noticeable in treatment guidance and what may be the most appropriate treatment methods. However, all are striving to improve your water quality.

Once you are aware of a problem with your water this is when you turn to the PWS industry for help.

Water treatment

“Correct and sensible interpretation of your water analysis is essential to achieve the best outcome”

You would expect to receive appropriate guidance from suppliers for a range of contaminates but this is not always the case.  Any treatment options must be carefully considered and a common error is to supply equipment based on one set of test results.

Private water supply in Norfolk

Test results are a snap shot of that particular moment and may not be truly ‘representative’ of your water. If a sample is taken immediately after a borehole is drilled or if there is a storage tank within the system then the results can be vastly different from the true nature of the supply.

It is imperative that the supply and your requirements are fully understood before committing to any equipment.

A very common scenario is that of the ‘turbidity’ filter.  Turbidity is the technical term for cloudy and often water samples containing high levels of Iron are also very turbid. This is due to the Iron oxidising and becoming visible.

This ‘turbidity’ result then leads suppliers to offer a filter dedicated to the turbidity plus an iron removal filter. In reality the water coming from the supply has no turbidity only Iron. The Iron removal filter is all that is required.

The point is; to make sure you are only getting what you need to make your water compliant. The best PWS is the one that needs no or as little treatment as possible!