The key with using water for a stop bath is to triple-rinse (completely filling the tank, agitating, and then emptying) the tanks with water before fixing. I work in the chemical industry and triple- rinsing is standard for everything we do to remove chemical residue from tanks, drums, and whatever.(posted 8269 days ago)Assume, for example, that a single rinse will conservatively remove 99.9% of the chemical from the tank. After three rinses, then, you have reduced the carry-over residue to 0.1% x 0.1% x 0.1% = 0.001% (one-thousandth of a percent). This is more than sufficient to prevent any appreciable cross-contamination.