In the water sector, a measure called the 'Security of Supply Index' is used to assess how capable each water company is of meeting customers' demand at present and in the future.
The measure is calculated by simulating the supply and demand figures for a dry year, or a drought, in order to determine the surplus or deficit that would exist in such conditions.
We agreed annual 'security of supply' targets with our regulator, Ofwat, in 2006. We met these targets in 2009/10, as in the previous two years, through cutting leakage, developing new water sources and by our customers reducing their water usage.
In the 12-month period, we surpassed our security of supply target of 85. Having closed the supply-demand gap in London, where we reached a score of 100 on the Security of Supply Index for our region – the maximum possible, and the first time we have done this.
During 2009/10, we implemented three new water resource schemes which between them provide an extra 167 million litres per day (Ml/d).
By far the largest of these is the Thames Gateway Water Treatment Works desalination plant, in east London.
The new works takes water from the tidal River Thames and has the capacity to provide water for up to approximately 400,000 households.
It uses a process called reverse osmosis to remove the salt and provide, at full capacity, 150 Ml/d of drinking water.
The works is the first large-scale desalination plant to be built in the UK and provides London with a much-needed back-up supply in the event of a drought.
On-site generators which can run on biodiesel (made from materials including used cooking oil) will produce enough renewable energy to power the works.
You can read more about the plant in the 'Water treatment works' section of our website.
The remaining extra 17 Ml/d comes from groundwater sources in Wanstead and the Stratford area.
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