What is a Private Water Supply?

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

Categories of Supplies

Private supplies are categorized according to the use and the quantity supplied. A supply only used for drinking, washing and cooking by the inhabitants of the properties served is a category one, whereas if the water is used in a B & B, tearoom, hospital, beverage or food production facility etc. will be category two.

Category one supplies are divided into six classes. The largest is class A serving more than 5000 people down to the smallest consisting of a single dwelling, which is class F. Category two is divided into five classes. Class 1 supplies more than 1000 cubic meters of water per day whereas the smallest, class 5, less than 2 cubic meters.

The local authority carry out water tests on a regular basis to ensure that they comply with quality standards, apart from class F supplies where no regular sampling and testing is required, although occasional checks are carried out. The highest categories and classes are tested 24 times a year whereas a category two, class 5 supply would be tested annually e.g. A small hotel.

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 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 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 traveling 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 unusual 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 well 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 the are usually constructed with concrete ring segments. High aquifers are more likely to suffer from microbiological contamination than deeper ones. It is also not unusual 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 maximize the water yield. During periods of high precipitation 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 not unusual 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 specialized 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 commonest causes of microbial contamination in boreholes is the ingress of surface and high level waters. It is not unusual to find the top of boreholes below ground level in a chamber that 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. It is not unusual to find the remains of small animals when pumps are lifted.

A carefully constructed borehole, drawing it's water from a confined aquifer and equipped with correctly installed headworks will inherently provide the purest water from a microbiological point of view.

The mineral content will depend on the make up 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. Granites and sandstones tend to yield soft and acidic water with low levels of minerals. Some waters are high in Manganese, Iron, Aluminium, Fluoride and Arsenic (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.