London is classed by the Environment Agency as 'seriously water stressed'. This is because the region's large population means that the amount of rainfall per person is very low.

London actually receives less rainfall per person than Rome, Istanbul, Dallas or Sydney.

The volume of water we can take from rivers and groundwater sources, to treat and turn into drinking water, is limited by licences from the Environment Agency. These controls are set in order to protect the environment.

Pressure on water resources will continue to grow in the future. Another 700,000 people are forecast to be living in London by 2021, and climate change will increase the likelihood of longer, hotter summers.

As London's water company, we have a responsibility to make sure there is always plenty of water to go round. We need to be able to meet our customers' needs, even during a long-term drought.

The ongoing replacement of London's leaky Victorian water mains has been a major success, helping to cut leakage by more than a quarter in the past five years.

We have also been working to encourage people to use water wisely.

However, the benefits of these activities are not enough to make sure London will have enough water in a drought.

We need to find new water sources to help increase certainty that we can supply all the water Londoners need to use, whatever the circumstances.

• Watch a short film about how the process works