We have a swimming pool & I have connected an old gutter pipe to one of the downpipes on the house closest to the pool. Everytime it rains, a substantial amount of water from the roof is diverted into the pool. All the other downpipes run into flower beds.
Incidentally, I keep a bucket in the kitchen sink. You'd be surprised at how much water goes into rinsing hands, cups & fruit & vegetables.

Good for you! Just remember that soapy water is not recommended for edibles and you should alternate with fresh water to flush away accumulated salts.

Soaker hoses and drip irrigation are much better for plant growth than overhead watering anyway, and save water to boot.

And mulching helps too. Here in CA we never get any rain half the year, and I keep my cottage garden looking beautiful with only watering twice a month.