"We must be rigorous in managing our water resources and be as economical as possible in order to make best use of the reserves still available," Environment Minister Nelly Olin said.

Curbs, including hosepipe bans, were now in force in 22 of mainland France's 96 departments, the ministry said.

"A risk of drought or damage to our lakes and rivers cannot be excluded if there's a prolonged lack of rain in the coming weeks as undergound water levels remain low," it said. Southwest departments affected by a lack of rain included some major growing areas for maize, which needs more water than other grains and is often irrigated.

After the heatwave of 2003, when thousands of mostly elderly people died, France had a dry 2004/05 winter and low rain in the 2005 autumn, leaving the water table depleted.

The country imposed rationing over around half the country last summer, with measures ranging from bans on car washing and filling swimming pools to limits on agricultural use.