The Environmental Protection Agency’s new administrator says unsafe drinking water is “probably the biggest environmental threat” the world faces.

Andrew Wheeler told CBS News in an interview airing Wednesday climate change is “an important issue” but most of the threats it poses are “50 to 75 years out” and it’s “unreasonable” for the 2020 Democratic candidates to focus so much on it.

Climate scientists see the necessity for broad and immediate action to address global warming. The United Nations says “now is the defining moment to do something about it.”

Wheeler was nominated by President Donald Trump and was confirmed last month. He acknowledges human behavior “certainly contributes to” climate change and says the U.S. is working to reduce carbon dioxide emissions.

Wheeler says 92 percent of the country’s water meets EPA safety standards every day.