It's only a "waste" if the water is scarce. People rarely talk about wasting air (except to call someone dumb) because the air is virtually unlimited.
For example in the UK it's damn near impossible to waste water because it rains so consistently. Water isn't scarce. You can't really waste it, because there's always plenty more.
Even if you could pipe the water from NYC all the way to CA it'd be prohibitively expensive.
So the only way this is "waste" is if it's depleting the aquifer faster than it replenishes. That's possible of course. But unlikely, because NYC has been huge for hundreds of years now. If they're depleting aquifers it's only very slowly.