LONDON — The U.K. may be known for its gray skies and near-constant drizzle, but the head of the island nation's environment agency has warned that it could run out of fresh water within 25 years.

"We won't have long-term water security unless all of us change our behavior," the chief executive of the U.K. Environment Agency, James Bevan, said in a speech Tuesday at a conference in London.

Climate change and population growth will cause severe water shortages, and by 2050 dry summers could result in up to 80 percent less water in some of the country's rivers, he said.

The country relies on fresh water from rivers, lakes, reservoirs and groundwater, and climate change makes this supply less reliable. Also, winter rainfall has increased in recent years while summers are becoming drier, posing a risk for both floods and droughts, according to a 2018 study by the agency.

Already, the vital resource is falling short of demand. More than a quarter of groundwater sources and 18 percent of surface water sources were extracted beyond a sustainable level in 2017, the agency reported.

Climate change is not the only factor draining the supply.

Britons use an average of 37 gallons of water per person daily. Bevan said that far exceeds the amount used in communities in Denmark, where the average is only 21 gallons.

The overall demand for water is poised to grow as the population is expected to increase by 8 million from the current 67 million by 2050, he said.

Moreover, old infrastructure is contributing to water waste. Nearly 800 million gallons of water — enough to support 20 million people — are lost daily through leakages, the agency has reported.

And it's not just people and industry that will suffer under water shortages: Wildlife, including fish, are under threat if these resources dry up.

An empty Wentwood Reservoir in South Wales. David Goddard / Getty Images file

Bevan described the crossroad of pressures on water as "the jaws of death," but said there is still time to avoid the worst crises.

A system of water sharing could have regions with stable supplies relieve other areas of the country facing shortages, such as the southeast where the highest concentration of people live, he said.

New reservoirs and more desalination plants would increase the supply of fresh water, he said. Repairing old systems to scale back just half of the current leakages would also make a significant difference.

While new infrastructure is costly, he said the price tag of preventative interventions is about half the roughly $54 million incurred as a result of extreme drought.

Tougher policies on water usage by industries and incentives for water-efficient household products like toilets and dishwashers can help reduce consumption, he said. Individual actions such as not watering the lawn could help reach current targets of lowering average consumption to 26 gallons daily, relieving pressure on the environment.

"We need to change our attitudes to wasting water so it becomes as socially unacceptable as throwing your plastic bags into the sea," he said. "We need to use less water and use it more efficiently."