We live in an area surrounded by grass fed cows, so what does it matter if we throw away 3/4 of our steak?
Without regard to how plentiful resources are in our particular area, being needlessly wasteful is in bad taste more than anything. It's a lack of appreciation of the value of what we have.
For water specifically - it is generally speaking the most valuable resource available, we just don't appreciate it because we happen to have a lot of it.