51�Թ�

Analyzing data for large sewage treatment plants in seven states that rely on Colorado River water, the researchers found California is recycling only 22% of its treated wastewater.

The firm has been heavily criticised for sewage spills, and is also struggling to fix leaks and modernise outdated infrastructure.

The analysis, which the BBC had exclusive access to, used United Utilities operational data to establish when the company was discharging sewage into Windermere when it should by law have been treating some of it.

The company extracted profit while pipes leaked and sewage poured into rivers.

Water UK, the industry body, said sewage spills are a "disgrace" but has committed to a programme of investment worth £104bn over the next five years.