With each flush, much water goes through the toilet refill tube and down the overflow tube. I measured it today and it was 6 cups for one flush. The first cup is certainly wasted because the flapper is up while the water is spraying into the overflow tube.
1.5 quarts per flush seems like a lot of wasted water in my house alone, not to mention nationwide and worldwide.
What approaches might I try to reduce the amount of unneeded water directed down the overflow tube?
Update: I just moved the refill tube so that all the water is redirected into the tank and none into the overflow tube. That saves about 1.5 quart per flush. The toilet seems to flush just as before. The water level in the bowl is unchanged. It seems not all toilets need the extra water that the refill tube directs into the bowl, but all flushing mechanisms of this type assume there is such a need.
Update a few weeks later: The water from the refill tube works in two ways. It contributes to the water that flushes the waste and also contributes to the clean water that remains in the bowl after the flush. When I redirected the refill tube in on toilet, the toilet did not flush effectively. The water in the tank was an inch or so below the manufacture's line. So I will adjust the tank float so the toilet flushes correctly but save the water that exits the refill tube while the tank is refilling.