ELI5: Explain Like I'm 5

Peak water

Peak Water is when we've used up too much of the Earth's water and it is running out. It's like filling up a cup of water: if you keep drinking from it, eventually there won't be any left. The Earth's water supply, just like any cup of water, only has so much to offer, and when that amount is used up we call it "peak water" because after that point there won't be any more.