Throwing water on the hot rocks to generate some steam in the hot room is great. You mix a little bit of spearmint or something in to the water, throw a ladle full of water on to the rocks and hear it sizzle like a skillet. You get back on the bench and wait for that hot steam wave to heat you in the face and hang around for about a minute. However, when you use water from the tap, the chlorine, and whatever else the city puts in the water comes along for the ride. When that wave of humidity comes around-- you know something isn't right. You can smell the odd odor coming from the evaporated water.
To solve that-- I tried using filtered water from the store. For a couple of dollars, you get great steam that smells like the scent of spearmint that you added to it, rather than something else. It's also easier on the lungs.
Documenting how I built my outdoor wood burning sauna with photos, explanations and links to learn how to do it yourself.