My toilet is a modern one with a 7.5 litre cistern, and a two-stage flush. But the short flush is the one you get if you hold the button down, which seems daft to me, surely to take the action of a long flush should have to hold it down.
Fixing leaky pipes: definitely should be done. A certain amount of the water will find it's way into the wells and sinkholes, but still, not all of it and the effort to clean it has already been done.
Also, more efficient processing plants are very possible. My mate designs and commissions sewage and water treatment plants. He says that you usually have a sewage plant pumping clean, drinkable water into the river, and a mile downstream you have a water treatment plant pumping water out of the river, cleaning it all again and putting it into the supply. Waste of resources, might as well go straight from sewage plant to pumping station.
How many new houses have a grey-water system? Each morning 100-200 litres of water comes out of my shower nozzle... but enough about my early-morning pee.
Sorry! Anyway, 100-200 litres of water that isn't really that dirty, and could easily be used for flushing toilets or doing the first wash on a washing machine (3 inlets on future machines? hot, cold and grey?). The final rinse on the washing machine could also empty into the grey tank, perhaps the biological action might even help keep the tank fresh!
As for now, I'm flushing my toilet every time I use it, I'm not going to have a stinky wee-smelling bathroom just because Ken can't mobilise his Red Army into fixing some leaky pipes. Maybe I have a sensitive nose, but the smell of wee (such as when someone has forgotten to flush) makes me gag.