You're right of course....the poster is from the late 1800's when pollution wasn't a popular concern.... Using a folding basin, dip out the water, warm it if that is your preference, and take it 100'-200' away from the lake or stream. Soap (not 'bath bar') is completely biodegradable in soil. Use it to shave, shampoo, and wash up, and then dump the grey water in a cathole. I hate to stink, even out in the woods.