When plants undergo transpiration, they are returning water back to the atmosphere.
We require to keep our water supply clean because we imbibe that water. If our water supply wasn't unsullied, we would die of dehydration. Another reason is that without water, all the crops would die and we wouldn't have any aliment to victual and so we would withal die of hunger.
When referring to knowing where to find something when you need it you mean that you do not need a memorization of all things, you just need a source to find it when in need. I hope this answer suited your needs.
