If you join too many downspouts before they enter the cistern you could have a constriction that would be problematic.
Cistern no gutters.
I chose to use 2x6 material because i had it handy but if you choose to u.
The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel.
Traditionally this involves harvesting the rain from a roof.
Put them where they need to be.
This is a cistern i made from some pressure treated 2x6 material and a 55 gallon plastic juice drum.
Rainwater harvesting is collecting the run off from a structure or other impervious surface in order to store it for later use.
The water was collected from the roof gutters.
It is more important that you have unrestricted flow into the cistern.
The cistern typically located underground may be constructed of various materials including cinderblock reinforced concrete or precast concrete fiberglass or steel.
Install standard size mesh gutter covers over the entire gutter that will lead into the cistern.
A system of gutters and downspouts directs the rainwater collected by the roof to the storage cistern.
Sweep all debris from the roof and gutters leading to the chosen downspout by using a broom.
Remember that the x section of a 4 pipe is twice that of a 3 pipe.
The water might have been used by the household if there was no city water at the time.