Nitrates from plant decay or nitrate-based fertilisers can sometimes find their way into natural water supplies.
There's been considerable discussion over the years about the possibly harmful effects of nitrates in the water supply. On one hand, there is talk of a link between nitrates and cancer in animals. On the other hand, in East Anglia, where nitrate levels are relatively high, stomach cancer levels are lower than average for the UK. Nitrates have also been linked in the past to a very, very rare condition that affects some bottle-fed babies. There is, however, little hard evidence on either side.
The drinking water regulations call for a maximum of 50 milligrams per litre of nitrate in drinking water supplies. There may have been some infringements of this regulation in the past by some water supplies. Generally speaking, though, the necessary equipment has been, or is being, installed across the country to keep within the limit and infringements in mains water supplies are now rare.
If consumers are concerned about possible excessive nitrate levels in their water supply, they should contact their water supply company for an analysis of the water, or, in the case of a private (non-mains) supply such as a borehole or well, the local Environmental Health Officer.
If a consumer chooses to reduce nitrate levels, there are several plumbed-in drinking water filters available to do the job. Be aware, though, that there are many types of drinking water filters available, with different capabilities and only some will remove or reduce nitrate.
Nitrate removal filters use the ion exchange principal as with water softening, where media is "charged" with chloride from brine which are exchanged for nitrate ions in the water. When all the chloride ions have been used up, the system is "regenerated" automatically using brine, the nitrates being washed out of the filter, it is then ready to treat the next batch of water. Regeneration can be set up on either a time or flow basis dependent on the filter selected.
So, it is essential to use a reputable supplier to ensure you select a filter of suitable capacity and nitrate reduction capability. You should also ensure that the filter is supported by a performance validation and that you adhere rigorously to any maintenance instructions.