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.

In delivering our plan we have now commissioned our first nitrate removal plant, with a second currently under construction and due for completion this year.  We have also built a number of booster stations in our distribution network to ensure the treated water can get to where it is needed.  We plan to construct third nitrate removal plant before 2015.

To complement these treatment solutions we have undertaken a programme of catchment modelling to understand how nitrate travels from the land and through the aquifer to our sources. The detailed models that we have developed indicate that catchment measures on the land would not be effective in reducing the rise in nitrate over the next 25 years, which is due to application of nitrate on the land in the past.  As a result we have no current programme of catchment management, but continue to work closely with our stakeholders to protect our water supply sources from applications on the ground leaching into the aquifer.