A well-built borehole can provide decades of clean, reliable water, but it is never the same as mains water. Borehole water comes from deep in the rock, which protects it from much surface contamination but loads it with whatever the rock contains: iron, manganese, hardness, hydrogen sulphide and sometimes arsenic. This guide explains what to expect from borehole water, the rules that apply, and how to treat it.

At a glance

  • Typical issues: iron and manganese, hardness, hydrogen sulphide, occasionally nitrate or arsenic
  • Bacteria risk: lower than springs and shallow wells, but present if the headworks are poor
  • Typical treatment: sediment filtration, iron and manganese removal, softening, then UV disinfection

How a borehole works

A borehole is a narrow shaft drilled down into a water-bearing rock layer, called an aquifer, often tens of metres deep. The upper section is lined with casing and sealed with grout so surface water cannot run down the outside of the pipe. A submersible pump lifts water to a pressure vessel or storage tank, from which it feeds the property.

The headworks at the top of the borehole are critical. A sealed, raised cap inside a protected chamber keeps out surface water, insects and small animals. Most bacterial problems in boreholes come from damaged or poorly designed headworks rather than from the aquifer itself.

What is typically in borehole water?

Contaminant Why it occurs Treatment
Iron and manganese Dissolved from rock in low-oxygen groundwater; water comes out clear then stains orange or black Iron and manganese filters
Hardness Calcium and magnesium from limestone and chalk aquifers Water softener
Hydrogen sulphide Natural bacteria in low-oxygen groundwater; rotten egg smell H2S treatment
Nitrate Farmland above the aquifer; can take years to arrive Nitrate reduction or RO
Arsenic Natural in some geology Arsenic reduction
Bacteria Poor headworks, shallow casing or flooding Sediment filter and UV
Sediment Fine sand drawn in by the pump, especially in new boreholes Sediment filtration

Rules for boreholes

  • Abstraction licence. In England you can take up to 20 cubic metres a day without a licence; above that you are likely to need one from the Environment Agency. Check the government's guidance on whether you need a licence to abstract water, including whether you need consent to investigate before drilling.
  • Drilling records. Information on water boreholes deeper than 15 metres must be sent to the British Geological Survey, which your driller normally handles. Groundwater UK has a helpful guide to the process.
  • Water quality. Borehole water used for drinking falls under the Private Water Supplies (England) Regulations 2016. A supply for your own home is your responsibility; shared and commercial supplies are monitored by the local authority. See testing for landlords and businesses.

Wales, Scotland and Northern Ireland have their own regulators and rules, so check locally.

Testing borehole water

Test a new borehole before you design treatment, then retest once treatment is installed. After that, test for bacteria at least once a year and do a full chemical test every few years, since groundwater chemistry can change slowly over time. See private water supply testing and the results guide.

A typical borehole treatment system

  1. Coarse sediment filter to protect everything downstream.
  2. pH correction if the water is acidic. See acidic water.
  3. Iron, manganese and H2S filter where the test shows them.
  4. Softener or nitrate unit if needed.
  5. Fine sediment filter, typically 5 micron.
  6. UV disinfection as the final barrier.

Our step-by-step guide on how to purify well and borehole water explains why each stage sits where it does. Remember to size treatment for the pump's flow rate, not just household demand.

Related pages

Why Wrekin Water

Wrekin Water is a family run company based in Bettisfield, Shropshire, serving more than 50,000 customers over 15 years and rated Excellent on Trustpilot. We design borehole treatment from your test results and, in North Shropshire, can install it for you. Send us your results for a recommendation.

Frequently asked questions

Often it is, but you cannot assume so. Borehole water is protected from much surface contamination but can contain bacteria if the headworks are poor, and frequently contains iron, manganese, hardness or other minerals from the rock. A laboratory test tells you whether it is safe and what treatment it needs.

In England you can abstract up to 20 cubic metres a day without a licence, which covers a typical household. Above that you are likely to need an abstraction licence from the Environment Agency, and you may need consent to investigate before drilling.

Borehole water often contains dissolved iron, which is invisible underground but oxidises into orange-brown particles when it meets air. An iron and manganese filter removes it.

It depends on the test, but a typical system includes sediment filtration, iron and manganese removal, softening where the water is hard, and UV disinfection last. Some boreholes also need pH correction or nitrate treatment.

Test before designing treatment and again once it is installed. After that, test for bacteria at least once a year and do a full chemical test every few years or whenever the water changes.