Depends what you mean by &quot;sustainable&quot;.<p>There&#x27;s far more fresh water falling on the US than is being &quot;used&quot;. Go look at any river. Gazillions of litres of fresh water per minute just flowing out to sea and getting salty. Then imagine the number of rivers doing that.<p>Of course damming every river and diverting it to other uses is impractical and would have bad effects on various ecosystems, but there&#x27;s a lot of spare fresh water just running out to sea.<p>And then remember that the vast majority of the water that we &quot;use&quot; is not getting split into hydrogen and oxygen, it&#x27;s staying molecular water and it&#x27;s hanging around.