I was able to purchase a used water meter for $35 from our utility company about 10 years ago. We have it hooked onto the primary source of water for our yard -- we have a spigot in the front that is not covered. We installed it ourselves, it was a simple installation.

We get a deduction in the sewer fee only. It has saved us quite a bit over the years, but less so now that we have a gravity fed rain barrel watering system for the garden.

So much will depend on how your utility handles the system. I'm in Maine so our water costs are low.