Nobody seriously paused to think about the different functions and their needs; they just took the position that if water comes in and water goes out, it is all pretty much the same and should be in the same room. Nobody thought about how the water from a shower or bathtub (greywater) is different from the water from a toilet (blackwater); it all just went down the same drain which connected to the same sewer pipe that gathered the rainwater from the streets, and carried it away to be dumped in the river or lake.
It is hard to find something that we actually got right in the modern bathroom. The toilet is too high (our bodies were designed to squat), the sink is too low and almost useless; the shower is a deathtrap (an American dies every day from bath or shower accidents). We fill this tiny, inadequately ventilated room with toxic chemicals ranging from nail polish to tile cleaners. We flush the toilet and send bacteria into the air, with our toothbrush in a cup a few feet away. We take millions of gallons of fresh water and contaminate it with toxic chemicals, human waste, antibiotics and birth control hormones in quantities large enough to change the gender of fish.
We mix up all our bodily functions in a machine designed by engineers on the basis of the plumbing system, not human needs. The result is a toxic output of contaminated water, questionable air quality and incredible waste. We just can’t afford to do it this way any more.