Nitrate levels in many waters are often high. The legal limit in Ireland is 50 mg/l as nitrate (NO3).
Over 60% of nitrate enters water from agricultural land. High concentrations of nitrate in water can cause methaemoglobinaemia in very young children (blue baby syndrome). In extreme cases this can be fatal.
The most common method of removing nitrates is ion exchange. Nitrate rich water passes over a resin where the nitrate is held. When the resin becomes saturated it is automatically regenerated with salt.