– To the casual observer, Britain — an island nation that’s no stranger to rain — could not get much wetter.

But, as it turns out, that’s a fallacy. And if preventive steps are not taken, in less than three decades, Britain might run out of water, the chief executive of the Environment Agency, a public body responsible for conservation in England, said Tuesday.

“On the present projections, many parts of our country will face significant water deficits by 2050, particularly in the southeast, where much of the U.K. population lives,” the agency chief, James Bevan, said at a conference on water use.

In about 20 to 25 years, demand could close in on supply in what Bevan called “the jaws of death — the point at which, unless we take action to change things, we will not have enough water to supply our needs.”

The reasons, he said, were climate change and population growth. And he called for a change of attitude toward water conservation to help tackle the problem.

“We need water wastage to be as socially unacceptable as blowing smoke in the face of a baby or throwing your plastic bags into the sea,” Bevan said.

Many in Britain, citing the often rainy weather and expressing frustration with the infamously high levels of leakage from underground pipes, tend to belittle warnings about water shortages.

But climate change means that Britain “will have hotter and drier summers,” Bevan said. Last summer, the country was hit with weeks of unusual heat and unusually dry weather.

In the future, the changed conditions could amount to a 10 to 15 percent decline in the available water, and rainfall will probably become less predictable, creating a higher risk of drought. At the same time, Britain’s population is expected to rise by 8 million in the next three decades, to 75 million in 2050, from about 67 million now.

“Climate change plus growth equals an existential threat,” Bevan said.

To avoid severe water shortages, he added, demand would have to be reduced — by taking measures like cutting down on leakage, increasing metering, having sustainable drainage systems and cutting down personal use — and the supply would have to be expanded.

“We can increase supply by a mix of methods, all of which we’ll need to pursue,” Bevan said. Those include building more desalination plants, transferring water from surplus to deficit areas and building reservoirs, he said.