This is a cistern i made from some pressure treated 2x6 material and a 55 gallon plastic juice drum.
Cistern no gutters.
The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel.
The water was collected from the roof gutters.
The water might have been used by the household if there was no city water at the time.
It is more important that you have unrestricted flow into the cistern.
If you join too many downspouts before they enter the cistern you could have a constriction that would be problematic.
Sweep all debris from the roof and gutters leading to the chosen downspout by using a broom.
A system of gutters and downspouts directs the rainwater collected by the roof to the storage cistern.
Remember that the x section of a 4 pipe is twice that of a 3 pipe.
Put them where they need to be.
I got the used drum locally for 15 and the wood came from my scrap bin.
Cistern covers are 2 x2 and are cast in the floor.
I chose to use 2x6 material because i had it handy but if you choose to u.
A cistern is an underground tank for storing water.
The cistern typically located underground may be constructed of various materials including cinderblock reinforced concrete or precast concrete fiberglass or steel.