A lot of public policy work is figuring out how to achieve a certain goal without directly mandating a particular action.

For example, what if water wasn't billed at a flat rate? Each building could have an allotment based on size and expected occupancy. One rate within that amount, and a higher rate for each unit over it. Calculate the level such that essential water usage is affordable and watering a large lawn becomes a luxury.

I doubt that exact plan is workable without further elaboration; the law of unintended consequences is powerful. But the point is that "we should have more sustainable landscaping" doesn't necessarily equate directly to "ban all grass".