Even if you have been drinking from your supply for years, you can't be sure it's safe just by looking at it.
Although it might look, smell and taste clean, it can still carry impurities that could put people at risk, particularly those who are more vulnerable to illnesses, like children and older people.
Having your supply checked
You must have your private water supply checked regularly to make sure it's safe.
Your local council's environmental health department is responsible for monitoring water quality. Contact them if you're looking for advice about your supply.
Larger supplies are checked annually as a matter of course. But if your supply is small, or you're the only user, you'll need to contact your council and ask for it to be tested.
If your drinking water changes colour
If your drinking water changes colour, especially after heavy rainfall, it may have been contaminated by soil, blue green algae or surface waters that have got into your supply, and it might be carrying harmful bugs.
If your supply has an unusual smell, or taste, have it checked. And if it's contaminated, have it treated immediately.
You might want to use bottled water until it can be checked properly.
If you decide to keep using your supply while it's discoloured, you should always boil it before using it.
You should also run your taps until the water becomes clear again.
Common illnesses associated with private water supplies
E. coli bacteria live in animals' intestines, including humans.
If any amount of E. coli bacteria is found in a water sample, it shows that human sewage or animal faeces has contaminated the supply.
VTEC and STEC are particular types of E.coli that can cause serious illness to humans.
Some people who are infected may not have any symptoms, but an infection can cause kidney failure or even death. Young children and older adults are most at risk.
Germs like E.coli, VTEC or Cryptosporidium, are commonly carried by farm animals. These germs can be present anywhere in the outdoors and may contaminate your water.
Only a few bugs are needed to cause an infection, and it's not something you can build up an immunity to.
To avoid an E.coli infection, don't drink water from sources such as rivers, streams and lochs without treating it first.
You should also make sure that your water source, or borehole, is properly sealed, and you should wash your hands thoroughly using running warm water and liquid soap.
Other gastrointestinal and stomach illnesses
Other bugs from human sewerage or animal faeces can contaminate your private water supply and cause gastrointestinal illness include:
The health effects of drinking contaminated water can range from no physical impact, to severe illness or even death.
Some of the symptoms of gastrointestinal infection from drinking contaminated water can be immediate, or may happen a few weeks later.
This is a parasite which can be found in human and animal waste.
Most healthy people recover from cryptosporidiosis infection within a few weeks. But it's a particular threat to people whose immune systems have been weakened by other illnesses, like HIV/AIDS, or certain treatments.
If your immune system has been weakened and you're at risk of a serious illness, you should boil all your drinking water, no matter where it comes from.
To avoid a cryptosporidium infection, don't drink water from sources such as rivers, streams and lochs without treating it first.
You should also make sure that your water source or borehole are properly sealed, and you should wash your hands thoroughly using running warm water and liquid soap.
Chemical poisoning from pesticides or nitrate
The presence of high levels of nitrates in well water is usually the result of farming activities like fertilizing, or seepage from septic systems.
If nitrates are at levels above 10 milligrams per litre of water, infants may suffer from a condition known as methaemoglobinaemia, or 'blue baby syndrome'.
This syndrome is caused by the nitrates interfering with the blood's ability to carry oxygen throughout the body.
Regular intake of even low levels of lead can have negative effects on your health, especially on brain development in babies in the womb, infants and young children.
Drinking rain water
You can collect rain water for non-drinking purposes like watering your garden or flushing your toilet, but there are better water sources for drinking water.
Rainwater quality is variable and it's hard to know for sure what contaminants are in it. This makes it difficult to plan a treatment system that means it's always safe to drink.
UV filtration is used on other private supplies such as boreholes or well water, but these sources tend to be fairly consistent in the kind of bacteria and metals contained in them.
So it's better to get drinking water from a traditional private water source.
Reducing the risk of contamination
There are also some simple steps you can take to lower the risk of your water supply becoming contaminated.
- make sure the water source is protected from contamination by grazing animals, or material washing down from upstream
- install and maintain appropriate treatment that can treat your water to a consistently safe quality
- ensure your water is properly disinfected before you use it
- make sure that water is stored and distributed in a way that avoids it becoming contaminated after treatment and disinfection, but before you consume it
- make sure all covers for your supply are properly sealed
- raise covers above the level of the land
- cover the ends of inlet pipes with fine mesh
- talk to local farmers to make sure there are plans to avoid contamination, and protect the supply from contamination by other chemicals, especially agricultural pesticides, oil, solvents and industrial chemicals
- make sure tanks and pipework are protected from exposure to chemical spillages and accidental contamination. Especially if supply pipes are made of plastic or polypropylene