Nitrates

Over the past 30 years Cambridge Water has recorded a steady increase in nitrate levels in samples taken from customers' taps.

Nitrate is an essential nutrient for the growth of many types of plant. It occurs naturally in many types of fruit and vegetables - often in quite large amounts - for example in carrots and oranges.

While nitrates are naturally present in soils they are also added by farmers in fertilisers to improve their crop yield.

Because nitrates are soluble they can be washed into rivers and streams or seep through the ground into underground water sources. This can take anything from weeks to many years, depending on how fast the water penetrates through the rock.

Under the Water Supply (Water Quality) Regulations 2000 (amendment) Regulations 2007 water is deemed to be wholesome if the level of nitrate does not exceed 50mg/l (50 parts in a 1000).

To date the issue of nitrates in the water has been dealt with by blending water from high nitrate sources with that drawn from sources with lower nitrate concentration, to ensure overall levels fall within those specified by Drinking Water Inspectorate.

However, detailed analysis of data taken from routine samples has given us a clear indication that chemical quality and an ability to comply with the water quality nitrate standard is likely to fail during the next five years, as nitrate levels continue to increase.

As it is not possible to blend our water further we have had to look at alternative measures to blending.

Cambridge Water has engaged stakeholders and gained support from the Drinking Water Inspectorate and the Environment Agency for a £8.3m strategy to manage increasing nitrate levels. Known as the Quality Enhancement Programme this will delivered in a twin-track approach between 2010 and 2015.

Firstly we plan to construct five nitrate removal plants requiring a capital investment of £7.8m and annual operating costs of £0.75m at the beginning of 2015 when all plants are operational. In total these plants will give the company an additional 40Ml/d of lower nitrate blend water, which will ensure we meet the regulatory requirement of 50mg/l. Secondly we will look to invest £530,000 in a catchment management strategy which will look at ways of ensuring less nitrate is leached into our supply network. Our aim is to understand more about how nitrates get into the ground and we envisage we will be working closely with farmers.

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