Scott Adams, the former engineer cartoonist who writes Dilbert, predicts that the next crisis will be a water shortage. I can believe this, with more and more regions worried about not having enough clean and potable water to get by. For all my life, my birth region of southern California has imported all its drinking water from northern California, which in turn has been importing it from northwestern California. All regions that I know of are straining their dwindling resources on this matter.
Only a tiny amount of this is due to direct human consumption. I personally drink about 1 gallon per day, but bathe (~60 gallons), wash (~20 gallons), and water (~50 gallons?) far more. The thirstiest work of all being agriculture, since all plants are quite thirsty, and animals often even moreso. A cow can drink it's own weight in water every week, in addition to needing to water its food, wash the cow, and so on.
This seems deeply ironic, because the earth is some 75% covered in water. However, much of this is the salt water of the ocean, useful for neither drinking nor washing. We humans are animals that must remain isotonic, that is, having the "same" volume of salt inside and outside our cells, to survive. Drinking salt water would only serve to strain your kidneys and make you thirstier still. Washing with salt water would render your cleaning agents useless, as well as leave a corrosive salty deposit covering the surface of whatever you washed.
Some of what remains is too polluted to drink. Many bodies of water in the US are contaminated with various chemicals, such as PCBs, mine tailings, and pesticides, and no longer fit for human consumption. Many others have an excess population of bacteria, amoebas, and other microorganisms that render drinking them unsafe.
There are ways to clean this water, but all of them are expensive, impractical, and require considerable energy input. So anytime we pollute water, we're really shooting ourselves in the foot. Other techniques are politically unfeasable, like water reprocessing. Australia is a very thirsty desert continent, but it can't reprocess the used water because that disgusts people. Any government that tried would see itself promptly losing the next election.
We should invest in water-processing technology, that we might all have non-vile water for our uses. We should also refill the various resource's we've been tapping, lest they all run dry. Perhaps we can refill lakes with reprocessed water, as the lake's native life does not know or care where it's water has been, whereas the human population definitely does.