More than a quarter of all water companies in England and Wales failed to do enough to manage leakage, regulator Ofwat has said.
Although companies continued to provide a good service to most consumers, six out of 21 companies failed to meet their leakage targets, according to the regulator's annual report.
The worst offender was Yorkshire Water, which lost on average 295 million litres a day in the 2009/10 period, Ofwat said.
Other companies which missed their targets were Cambridge, Dee Valley, Northumbrian, Southern and Veolia Central.
All companies met their annual leakage targets in the previous two years. This is the first time so many have failed to hit them.
However, the report said the failures occurred in the context of the coldest winter for more than 30 years, when snow-covered ground could make identifying leaks more difficult.
Companies reported high numbers of burst pipes because of ground movement caused by freezes and thaws.
Ofwat chief executive Regina Finn said failing companies would be forced to improve.
She said: "We take any leakage failures seriously. Most companies stepped up to the challenge of tackling leakage during a particularly harsh winter. Those who haven't, we have put on notice.
"If companies continue to underperform, we will take action. In the last five years, companies have had to pay out more than £500 million from their own pockets following underperformance. We've made sure that the bulk of this money has been spent on giving something back to customers, either through reduced bills or investment in improving services."
