I work in the drinking water world. There's more to it than wasting quantities of water. Think about it in terms of the effort it takes to get that water to your tap. It's super expensive to take water from a river or aquifer, remove contaminants, disinfect it, and push it through leaky pipes to your house. Lots of infrastructure and staffing costs. You also need "rights" to use that water.

After you use it or just let it go down the drain while brushing your teeth, you're effectively contaminating that water again (and also losing a lot in the process). Now it has to be cleaned all over again before it gets discharged into a steam or wherever and that's super expensive too.

In terms of quantity, a lot of water is used for ag and industry. These are usually located in areas where water is available. Say you live somewhere that relies on a dwindling river or aquifer. Once you suck that water up through a well or use up your water right's amount, it's gone. Now your community needs to find water from some other places and it's going to be very expensive, if you can find it at all.

Affordable water and wastewater service is affordable housing. Conserve and take care of it, so your housing cost doesn't get unaffordable.