Your kids use a lot of water because, where you live it is probably a way of life. When/if your kids goto school in california, they’ll adopt a California style. Recycle, reuse, reduce. Everyone in California has two trash cans and the recycle on is always overflowing. When I moved to Florida I was shocked that many of my neighbors didn’t even put out a recycle bin.
Your kids won’t go thirsty, but I bet you will notice a difference in shower length and other habits when they come home.