Here a well is $20-$25k. I've owned more than one and because all the water here has high TDS and is really hard, it's difficult water to deal with.
When I decided to build a house, I went GJ style and built a live-in shop first. Part of that shop design was supplying the water infrastructure for the residence. We decided to do water collection - and ran the math on what we need in terms of roof area and storage for our water use. There are spreadsheets that can help.
We currently store 15,000 gallons of water in 3 tanks. The tanks are interconnected on 2" valves and water seeks "level" so we can balance water across all 3 tanks as well as keep a reserve. We can direct the pump to pull from any specific tank by cutting off the other two.
I've had a lab look at the water and it's vastly better than what we pull out of the ground here. We don't need softeners.
What do you need for this to be a viable water source?
- First flush filters (these are simple mechanical devices that "drops" the first gallons of water when it starts to rain)
- Sediment filters (pre pump and post pump)
- We use UV to make the water safe to drink. IE - kill anything that might be living in the water
The best place to get the "cleanest" water is in the center of the tank. We use a 2" inlet hose (spa hose) with a filter that is sunk just under a float in one tank.
What have the problems been:
- Any exposed pipe can have freeze issues. Our system took damage under a rare heavy snow. I should have opened the flush filters 100% and drained any exposed pipe. Note, I'm in the south and we don't get long week or more freezes.
- In a downpour, you need huge pipe capacity. 4" pipe won't do it from 2 gutters.
- PVC may not be the right material long term (UV exposure)
- We can have droughts. This is our only water source short of begging from the neighbors. 15k gallons is the right math for droughts, but it's too tight for me. But I've added another 2 tanks and will collecting water off the residence. 25,000 gallons total.