What it is
Ammonium is the dissolved form of ammonia, a nitrogen compound. It is the first stage in the breakdown of animal and plant waste, so it points to recent contamination.
Where it comes from
The usual sources are septic tanks, slurry, manure and fertiliser reaching a well or borehole, and bacterial activity in stagnant parts of the system. Some deep groundwaters contain natural ammonium from peat and organic deposits.
Why it matters
Ammonium itself is not harmful at the levels found in water. It matters because it indicates contamination, because it can be converted to nitrite in the system, and because it interferes with chlorine disinfection, making it less effective. A result over the guideline is a prompt to look at the microbiological results closely.
What can be done about it
First find the route in and close it. Ammonium itself can be removed by biological filtration, ion exchange or chlorination to breakpoint, with the choice depending on the level and the rest of the water chemistry. A retest after the work confirms the result.
Information last reviewed 5 October 2026 by Pozzani Pure Water.