The more water, the better POTENTIAL wash, but design is more important. The Toto dual cyclone bowls have better wash, with less water. NONE of the toilets will wash the bowls as well as those from 30+years ago when they might have used 7-8 gallons to flush, but the dual cyclone is pretty slick for what it does. The inclusion of the super smooth glazing (Toto's SanaGlos) helps, too, as stuff has a much harder time sticking in the first place.