Thames Water today reassured its 8.8 million customers that hosepipe bans are unlikely this year, despite supplies starting to drop.
Thames, which serves London and the Thames Valley, said its reservoirs are 90% full, but urged customers to be careful in their water use as it is too early to predict what the weather will be like over summer.
Chief executive Martin Baggs said: "While it is unlikely we will need to impose any restrictions this year, we would always urge our customers to use water wisely."
The group, which is owned by a consortium of pension funds and infrastructure fund managers, added it had met its leakage targets for the fifth year running despite the coldest temperatures recorded in its 20,000 miles of pipework and a four-fold increase in the number of burst pipes.
Thames said it surpassed regulator Ofwat's leakage target by nine million litres per day, the equivalent of four Olympic-sized swimming pools, while the group also hit water efficiency targets for last year by reducing usage by five million litres per day.
Thames said pre-tax profits more than halved in the year to the end of March to £208.5 million, down from £453.6 million the previous year, as the group absorbed the new price regime for the five years to 2015 imposed by Ofwat.
Thames Water's reassurances on hosepipe bans came as a state of drought was officially declared in some parts of the country following the driest spring since records began.
Cambridgeshire, Northamptonshire and Lincolnshire are officially suffering from drought, while parts of the South West, South East, Midlands and Wales are experiencing near-drought conditions, the Department for Environment, Food and Rural Affairs (Defra) said.
The owner of South West Water - Pennon - said it did not expect to enforce a hosepipe ban this summer, but Severn Trent Water, which has eight million customers from Bristol to the East Midlands, has warned households they may face restrictions.
Mr Baggs said Thames Water supplies were starting to drop and urged customers to be cautious with their water usage. He said: "After a very cold winter, we now face the prospect of a very dry summer.
"In the same way everyone pulled together to help us tackle leaking pipes, we now need to ask our 8.8 million water customers to be careful about the amount of water they use."
He added: "It has been so dry that the water available to us from rivers and the underground aquifers is starting to drop, and we simply don't know what the weather will bring."