Bacteria are the one problem in well water you can't see, smell or taste. The water can look perfect and still fail a test. If your lab report shows E. coli or coliforms, this is what it means and what to do about it.
What the result means
- E. coli comes from the gut of people and animals. Finding any in a sample means the well has been contaminated by sewage or animal waste.
- Coliforms are a wider group of bacteria found in soil and surface water. Finding them means water from the surface is getting into the well.
The standard for drinking water is none of either in a 100 ml sample. There is no safe low number.
What to do straight away
Stop drinking the water untreated. Boil it and let it cool, or use bottled water, for drinking, making up infant feeds, brushing teeth and preparing food that won't be cooked. Take extra care for babies, older people and anyone who is unwell.
Where it comes from
- A septic tank or percolation area too close to the well, or not working properly
- Livestock, slurry or manure near the well
- Surface water running in after heavy rain, through a damaged cap, a cracked lining or a wellhead that sits below ground level
Fixing it takes two things
1. Look after the well itself. The wellhead should be capped, sealed and standing above the ground, with animals kept away from it. The well and pipework can then be disinfected with chlorine (bleach), which is often called shock chlorination. That deals with the bacteria that are there today. It doesn't stop them getting in again.
2. Fit ongoing protection. A UV disinfection system goes on the main supply into the house. The water passes an ultraviolet lamp that kills the bacteria as it flows by. Nothing is added to the water and it doesn't change the taste.
What a UV system needs to work
- Clear water. Sediment shields bacteria from the light, so a sediment filter goes in front of the lamp.
- Iron, manganese and hardness dealt with first. They coat the glass sleeve around the lamp and block the light.
- The right size. It has to match the fastest flow the house will draw, not the size of the house.
- A new lamp once a year. The lamp keeps glowing long after it has stopped doing its job.
Test again afterwards
Once the system is running, send another sample to the lab. A clear report is the proof. The EPA advises testing a private well at least once a year, because well water changes.
What to do next
We don't test water ourselves; an independent, accredited laboratory does that. Send us the report through our well water treatment page and we'll specify the treatment your water needs. Our own plumbers fit and service it.
Also on well water: iron in well water and rotten egg smell from well water.