Water taken from a stream, river, pond or lake is the highest-risk private supply there is. Unlike groundwater, surface water has had no filtering through soil and rock, so it carries whatever the land around it carries: silt, leaves, animal waste, bacteria and parasites. It can be made safe for drinking, but it needs more thorough treatment and more careful maintenance than any other source.
At a glance
- Typical issues: bacteria and parasites, heavy sediment and turbidity, colour, algae
- Bacteria risk: very high; assume it is contaminated until proven otherwise
- Typical treatment: settling, staged filtration down to fine microns, then UV disinfection
Why surface water needs more treatment
- Parasites as well as bacteria. Streams and rivers can carry protozoa such as Cryptosporidium and Giardia from livestock and wildlife. These are resistant to chlorine, but UV disinfection is effective against them when the water is clear.
- Rapid changes. A clear stream can turn brown within hours of heavy rain, carrying a surge of silt and contamination.
- High particle loads. Silt, leaves and organic matter block filters quickly and shield micro-organisms from UV light, so pre-treatment has to be much more robust than on a borehole.
- Algae. Ponds and lakes can grow algae in warm weather. Some blue-green algae produce toxins that UV does not remove, so avoid drawing water during a bloom and seek specialist advice.
Designing the intake
Good treatment starts at the intake. Draw water from a point that stays submerged but sits clear of the bottom sediment, screen it against debris and fish, and protect it from livestock. Many surface supplies use a settling tank so heavier silt can drop out before the water reaches the filters, which greatly extends filter life.
A typical surface water treatment system
- Intake screen and settling tank to remove debris and heavy silt.
- Bag or coarse filtration to take out the bulk of the remaining particles. See bag filters.
- Staged cartridge filtration stepping down through finer ratings, for example to 5 micron, using sediment and pleated filters.
- Specific treatment such as pH correction or carbon for colour, taste and odour, if the test calls for it.
- UV disinfection sized for the peak flow, with a lamp-failure alarm and ideally an automatic shut-off so untreated water cannot pass. See UV systems.
Check pressure gauges across each filter stage, especially after rain, and change cartridges before they block. Our guide on how to purify private water explains why each stage sits where it does.
Rules for surface water supplies
- Water quality. Any surface water used for drinking, washing or food preparation is a private water supply under the Private Water Supplies (England) Regulations 2016 and must meet the same standards as mains water. Shared and commercial supplies are monitored by the local authority. See the Drinking Water Inspectorate's guidance.
- Abstraction. In England you can take up to 20 cubic metres a day without a licence; above that you are likely to need one. See check if you need a licence to abstract water.
Testing surface water
Test more often than you would a borehole: for bacteria several times a year and after heavy rain, plus regular checks that the UV unit is doing its job. A full chemical test helps size the filtration. See private water supply testing and the results guide.
Non-drinking uses
If you only use stream or pond water for irrigation, livestock or wash-down, a simpler system of screening and sediment filtration may be enough. Keep it completely separate from drinking water pipework and never connect it to the mains.
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. Surface water systems need careful design, so send us your test results and flow requirements and we will recommend a setup. In North Shropshire we can install it for you.