If your water heater is old (10+ years) and/or in bad shape, it can be full of deposits and in some cases corrosion. Apparently we’re all supposed to be bleeding a few gallons from our water heaters monthly to maintain them. I don’t know anyone who does.

Our water from the city is total crap (and also the most expensive I’ve had in my life), so we added a softener and then split all the drinking/cooking water sources off to a RO system. But I’m also the guy with infinite sparkling water on tap from the kegerator in my kitchen (again only a few hundred in equipment and then about $80/yr in CO2, most of which I had from my home brewing hobby anyway).