Hello, I am an environmental engineer sharing my design for a ~300 gallon IBC tote rainwater collection system. What makes this different and beneficial for self-sufficiency is the low cost per gallon. This tote also provides a large enough storage tank to use a dedicated irrigation pump for reuse. You could make this as simple or as complex as you wanted to.
IBC totes are frequently used for storing and transporting food grade materials, so there is an aftermarket for cheap used totes, you just have to verify what they were used for. I got this 275 gallon tote off of marketplace for $100 USD. It was previously used to transport food dye. They are highly durable because they're built out of HDPE and galvanized steel.
Other Materials:
Leaf filter, from $10 to $70 - my preference is the Leaf Eater Advanced ($66)
Downspout diverter, my preference is Earth minded Flexifit diverter ($20)
PVC pipe and valves, figure $50
Total entry cost including tank: $180 - $240
Optional:
Lid adapter for two inlet ports $10
1 HP irrigation pump $140
Discharge splitter $10
Wi-Fi controller $30
Piggy-back Level float, alternative controller $50
Ozone injector to keep the water fresh and odor free: $400 (luxury) JED Engineering model 203
Usually they are there to make sure the (storm water or mixed) sewerage systems get properly flushed. It's not as ridiculous as it sounds at first.
I think that might be mostly from inherited old regulations/infrastructure, as most modern policies revolve around having separate storm water and sewage system for the opposite reason, as they don't want all the extra rain water overflowing the sewage treatment systems
And yet they allow corporations to relentlessly pillage all water sources going 2-3x their paid water rights while the populations eat the costs and effects...
It is all excuses to increase water insecurity.
I understand some of the reasoning behind it, but it doesn't logically make much sense in the end, as if you collect rainwater, you're eventually going to return it later...
The water cycle ends with me.
I can't figure out what you mean.