The newest toilets use only 1.28 gallons per flush. They save water but they're not cheap. I'm testing new parts for Roto-Rooter and I recently replaced all of the guts inside the most used 1.6 gallon toilet in the house. I replaced the fill valve with a new valve that uses less water, has a leak detection system and automatically cleans the tank of scale and debris (not the bowl).
Next I installed a new dual-flush system that allows users to press one button for a low-power half flush that easily expels urine. A larger button handles solids and wads of toilet paper using a full flush. So far, so good. My toilet is now using a fraction of the water it used to at a fraction of the cost of a new toilet. This is one of the best bathroom plumbing solutions I ever saw and the most sensible toilet repair Cincinnati ever saw!
My water bills will no doubt reflect the savings. Soon a Boston plumber at a Roto-Rooter office and a Seattle plumber at Roto-Rooter and almost every location in between will be installing these and other sensible water-saving parts as we go greener than ever before.