500 flushes is less than a year for a toilet used twice a day (say before and after bed), I hope that coating is cheap, easy to apply, and doesn't create substantial pollution either as it is created or used. I hope the sewer system doesn't need to just add water as a result. Toilet water use doesn't seem like a big enough contributor to the problem that it's much use optimizing it in most places. But there are proba…
You only use toilet twice a day? Keep in mind you need to flush after pee too.
When you only have restricted water, you shouldn't flush after peeing. There's even a saying to help conserve water this way:
"If it's yellow, let it mellow".