Nitrate is one of the most common chemical problems in rural private water supplies, and you cannot see, smell or taste it. It comes mainly from farmland, and it matters most for households with young babies. Testing tells you if it is there, and nitrate-specific treatment brings it back under the legal limit.

At a glance

  • UK limit: 50 mg/l nitrate (as NO3); nitrite 0.50 mg/l at the tap
  • Most at risk: boreholes, wells and springs in arable and livestock farming areas
  • Signs: none; only a test will find it
  • Fix: nitrate reduction systems or reverse osmosis for drinking water

What is nitrate and where does it come from?

Nitrate is a form of nitrogen that plants use to grow. It dissolves easily in water, so whatever crops do not take up can wash down through the soil into groundwater, springs and streams. The main sources are:

  • Fertilisers spread on arable land and grassland.
  • Manure and slurry from livestock.
  • Septic tanks and soakaways close to the water source.
  • Ploughing of grassland, which releases nitrogen stored in the soil.

Large parts of England are designated as Nitrate Vulnerable Zones because of this. Nitrate can take years to move down through the rock to a borehole, so levels in groundwater may reflect land use from long ago and can rise slowly over time.

Is nitrate in drinking water harmful?

The main concern is for bottle-fed babies under about six months old. Their bodies can convert nitrate to nitrite, which reduces the blood's ability to carry oxygen, a condition called methaemoglobinaemia or "blue baby syndrome". The 50 mg/l limit set by the Water Supply (Water Quality) Regulations 2016 is designed to protect them. If your supply is over the limit, do not use it to make up infant formula.

Do not boil water to remove nitrate. Boiling evaporates some of the water and leaves the nitrate behind, so it actually concentrates it.

Nitrite has a much lower limit because it is more directly harmful. Nitrite in a supply usually points to recent organic contamination, so it is worth checking for bacteria at the same time.

How to test for nitrate

Nitrate is part of a standard private water supply test. Because levels can change with the seasons and farming calendar, a single good result is reassuring but not the end of the story; retest every few years, before a new baby arrives, and if land use nearby changes. Our results guide explains how to read the figure.

How to remove nitrate from water

Ordinary carbon filters, UV systems and water softeners do not remove nitrate. You need treatment designed for it:

  • Nitrate-selective ion exchange. A resin that swaps nitrate for chloride, regenerated with salt like a water softener. It can treat the whole house. See our nitrate reduction range.
  • Reverse osmosis. A reverse osmosis system under the kitchen sink removes most nitrate from drinking and cooking water, along with other dissolved contaminants. It is a cost-effective choice when only drinking water needs treating.

On a private supply with bacteria as well as nitrate, the nitrate stage goes before UV disinfection. We can help you put the right sequence together from your test results.

Related contaminants

Why Wrekin Water

Wrekin Water is a family run company based in Bettisfield, Shropshire, serving more than 50,000 customers over 15 years and rated Excellent on Trustpilot. Private water supplies are one of our specialist areas, and in North Shropshire we can install treatment for you. Send us your results and our team will recommend a system.

Frequently asked questions

The UK legal limit is 50 mg/l of nitrate. It is set mainly to protect bottle-fed babies under about six months old. If your water is over the limit, do not use it to make up infant formula.

No. Boiling evaporates some of the water and leaves the nitrate behind, so it makes the concentration higher, not lower.

Standard carbon filters, UV systems and water softeners do not remove nitrate. You need nitrate-selective ion exchange resin, which can treat the whole house, or a reverse osmosis system for drinking water.

Nitrate usually comes from fertiliser, manure and slurry used on nearby land, or from septic tanks close to the source. It dissolves easily and seeps down into groundwater, sometimes taking years to reach a borehole.

Yes. Water companies monitor nitrate and treat or blend water to keep it under the 50 mg/l limit. Private supplies have no such treatment, so owners need to test them.