You say that low flush toilets are not that useful, but what about all the other usage of water in the household (shower, dishwasher, laundry...)? Does that water also get filtered in the same way (and hence it doesn't matter if you use less of it) or that's a different system and it makes sense to use less? Well, it makes sense to use less anyway (financially), since that's the ways incentives are setup, but just wondering about the environmental benefits.First of all, it makes sense to use less water if you have a water meter and the cost of additional water ($) is not worth the benefit (happiness).
But, second, the entire concept of charging for water use needs to be put into the context of the water system, i.e., will water that goes down the toilet and drains be available, after treatment, in the environment (or as recycled water returned to customers for landscape irrigation or for drinking)? If that's true, then "efficiency" in terms of less water per shower, flush or wash will not really translate into any saved water.
Third, the real target for water savings should be outdoor use -- mostly landscaping -- since that water tends to evaporate and/or sink into the ground, from where it cannot be reused.
That's why I think that outdoor watering should attract a higher charge (scarcity) or ban (shortage). Water budgets, by the same logic, do not make sense if they "lock in" a certain allowance of water for landscaping. That's why they are a bad idea in water-scarce areas and a waste of time in water-abundant areas.
Bottom Line: Flushed water does not disappear, worthless. It has value because it can be used again.