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Private Water and Sewage glossary – common terms

Borehole  - a shaft mechanically bored for the purposes of water abstraction.  Usually the depth of the shaft is in the order of several magnitudes the width of the bore.  Sometimes referred to as wells, particularly in the USA and also borewells.


Well – typically a hand dug shaft, usually at least 1m wide and anything from 2-3 metres deep to as much as 20m.  Normally older construction and can be cut through rock (and unlined), stone lined, brick-lined or constructed from concrete rings.

Spring – a classic spring is where an aquifer breaks to surface.  Normally a catchment pit is constructed over the top to protect and collect the water into a chamber.  The construction and collection methods can vary greatly with springs, as can the actual source; it is not uncommon to find field drainage considered as a spring source.

pH correction – for most private supplies where pH correction is needed it is to raise the pH (making it more alkaline) of the water to make it less corrosive.  Low pH water can attack concrete structures and corrode metal fittings – most common is pin-holing in copper pipe work.  Additionally low pH water may leach heavy metals into the water.  Most pH correction treatment takes the form of a vessel filled with a sacrificial calcium-based media.

UV disinfection – this is the most common form of disinfection for private supplies.  The UV light damages the DNA of bacteria effectively killing it.  It is important that the water is free from suspended matter and turbidity to be effective.  Disinfection is also only present within the lamp unit – downstream the water has no residual disinfectant properties.  Note – UV lamp is sometimes wrongly termed UV filtration but there is no physical filtration present.

Filtration – the most common type of filtration for a small private supply is by cartridge filtration.  Cartridges are available in a range of different pore sizes and physically remove particulate matter.  Larger supplies may be fitted with media filters such as sand.  These require routine back-washing to maintain performance.

Cess pit – this is simply a tank collecting foul drainage with no outlet.  Under current Building Regulations a domestic tank should be sized to hold a minimum of 45 days storage.  Cess pits are exempt from environmental permitting.

Reed beds and Withy beds – most common is the horizontal flow reed bed – this works by the effluent entering one end of the bed, draining through a gravel bed planted with reeds and collecting into a chamber at the opposite end before typically discharging to watercourse.  Withy beds follow a similar design but may have multiple beds featuring willow as well as reeds.  Horizontal flow systems are rarely installed now and it is no longer permitted to discharge straight from a septic tank into a reed bed.  All existing and new reed bed and withy bed systems require environmental permitting.

Septic tank – this is tank that collects foul drainage and retains solids whilst letting liquid drain to a drainage field.  As indicated by the name, the effluent is septic (anaerobic) and damaging to the environment so it is important the drainage field works correctly.  Septic tanks can have single or multiple chambers and can be constructed from a variety of materials.  In almost all cases they will need emptying yearly (and evidence of doing so kept for inspection).  Most septic tanks will not need an environmental permit providing they comply with the general binding rules.

Sewage treatment plant – for most small installations where sewage treatment is needed it will be provided by a package sewage treatment plant.  There are many manufacturers who make package treatment plants but almost all systems work by retaining the solids within a primary chamber prior to secondary treatment.  The secondary treatment involves the effluent being exposed to air to encourage aerobic digestion allowing a better quality of effluent.  In many cases the discharge can be straight to watercourse and again, providing the discharge complies with the general binding rules, no environmental permit will be needed.

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