(Reuters) - Municipalities and irrigation districts in the western Canadian province of Alberta have agreed to use less water this summer to combat a severe ongoing drought, the provincial government said on Friday.

Environment Minister Rebecca Schulz said water license holders had signed news memorandums of understanding covering four river basins in the southern half of the province.

Alberta, which produces most of Canada's oil, natural gas and beef, plus big wheat and canola harvests, opened water-sharing negotiations among licence-holders for the first time in two decades as it entered its fourth year of drought this year.

The province relies on melting snow and precipitation for most of its water supply and has allocated water since 1894.

Under the new agreements, municipalities will voluntarily reduce water consumption by 5-10%, Schulz said, while industry will use the minimum amount of water needed for reliable operations.

Irrigation districts, which account for 46% of Alberta's water allocation, have also agreed to use less by allowing other water users to receive their share and then dividing up what is left.

The level of Alberta's snowpack - the snow that accumulated over the past winter - in the last week of April will be key to determining when the water-sharing agreements will need to be activated, Schulz said.

"These agreements will only be implemented or activated if they are needed, and they will be regularly adjusted as drought conditions change," she told a news conference.

Some municipalities had already begun proactively reducing water use, she added.

As of the end of March, 66% of Canada was classed as abnormally dry or in drought, according to Agriculture Canada, a slight improvement from February.

Schulz said Alberta appeared to have more water available this year than in 2001, the last time water-sharing negotiations took place.

Alex Ostrop, chair of the Alberta Irrigation Districts Association who farms in the upper Old Man river basin in south-western Alberta, expects to receive roughly half the usual water allocation.

"(That) will have a significant operational and economic impact on each affected irrigation farmer and they have spent the spring making tough decisions with respect to cropping and rotation," Ostrop told reporters.

(Reporting by Nia Williams in British Columbia; Editing by Richard Chang)

By Nia Williams