"rationing water by cost" Water is a Utility, same as Electric and Gas, it costs money to process it ready for delivery to homes. You should pay for what you use. Forced rationing only applies if there is shortage. This ensures that all get at least some of the available supply.
According to the Environment Agency around 30% of households have a water meter. That is hardly a small number of houses. In some areas, I expect where there are high water bills eg South West, that figure is over 50%. People in houses with a meter nearly always use less water.
My water meter cut my bill by quite a bit so I am in favour of it. It helps that there are only 2 of us living there so usage is low (and I have 5 water butts for the garden!). Larger families are less likely to be in favour because their usage would be so much more.
Of course, I may change my mind if I am ever rich enough to afford a house with a swimming pool. But I suppose if I am rich enough for a pool, water rates will be of no consequence.
I suppose I had better try again to find that leak in my garden pond. One of the great problems we have in the UK is that all our water is processed at very high cost to drinking standards yet only a small fraction is actually used for drinking purposes.
By coincidence Radio Devon had a piece on water saving this lunchtime. The SWW rep stated that 75% of houses in Devon have water meters and this is probably the highest ratio in the country. You can also get a separate sub-meter for the garden. The attraction of that is that there are no sewage/rainwater run off charges for that meter. However it was also stated that for most users this option was not economically viable.