In Tx there are a few household rainwater collection systems. There are many variations, but the basic design is similar to yours (i.e. roof collection system, tank (above or below ground), purification system, pump, etc). A simple system costs approx $5k. Since the rain is unreliable, the systems typically require a backup water source.
Some owners truck water in when their tanks are low. The cost for approx 2k gal of water is $200. This will last a family of 4 approx 1 mo. This is expensive.
There are many tanks (a natural drainage area which has been damn'ed up to hold water) for livestock. The shallow tanks often go dry during a drought.
The most common solution is to drill a well, typically 150-600' deep. The cost is $5-15k. You need to meet min lot size, offset requirements (from other wells, septic systems, lot boundary, etc) to drill a well. Many of the older, shallow wells are going dry as an area is developed. The people have to drill new wells or switch to another water source.
Communities in the country often have a single private shared well, similar to a mini public water system.
I have a well since there is no other water source available. There is a lot of water in my water table, but the water quality is poor and I have to filter the water to make it drinkable. I think the water is harming some of my garden plants. There is a lake across the street, I'm working on a system to use lake water for my garden. I've seen many wells with drinkable water right out of the ground, I wish mine was similar.
buene suerte.