dubai,

Even if you collected the water in a buried cistern system, you would still have to pump it out with a submersible pump to utilize the water. If you collected at the level of the roof, your psi without a pump is 5 psi if your roof is 10 feet above the ground. What do you want to do with the water? Aloha

Hello lehua,

Silly me I assumed people would understand that I want to use this water for the garden plants. The roof is approximately 12 feet above ground. Underground cistern is out of question because there's concrete foundation around the house and the house is surrounded by concrete fence/wall which also has concrete foundation, which leaves little non foundation space between the house and the fence, and also there's 4 rainwater pipes so this would involve a lot of work and expenses. I am not doing this to save the money, we get 20,000 gallons of free water per month, so I wanted to do it for the sake of the environment, freshwater is scarce in UAE, and desalinization is an expensive way to get it. We do have a pump that pumps underground water, but that water is salty so we only use it to water native plants such as our date palm and the shade trees we have in the front of the front fence. I was wondering if there's some kind of non-electric device that would let the water flow into a container near every drain (like I said there's 4 of them). I am asking for simple device/way because my husband would not cooperate (he's already complaining that my gardening is expensive).

dubai,

With the parameters you have set for yourself, I would recommend using the free water you get every month for your garden. Most people don't have that benefit. Most people use gravity flow rainwater do not have the negative parameters that you seem to have. The negative impact that you cause the environment by using pumped water is extremely small and warrants, in your extreme case, not thinking about. JMHO Aloha

dubai-gardener, let us say that you place a 30 gallon drum next to one of those drain pipes; and you make a watertight connection from drainpipe to the drum as close to the base as possible.
Do you see that as rain falls water will collect in the drum?
A consequence of this is, that the water will seek its own level in the drainpipe also. If the system is completely sealed, then rainwater will fill the drum and, having no place to go, will back up in the drainpipe all the way to the roof eventually!
In my mind's eye I see containers that will hold those 9000 gallons. These containers will be probably 3 feet high with as big a footprint as your yard space will allow. Bear in mind that the taller the container, the higher will be the level in the drainpipe after the containers become full.
A relief valve will be necessary to get rid of water in times of plentiful rainfall.
The containers will have a "service outlet" to a drip or other low volume irrigation system.

Hello ronalawn,

What you describe is what I was looking for but couldn't visualize it. The rain doesn't all come at once, I have three drain pipes, and the nine thousand figure is the maximum possible, so in reality it would probably be less. Since it still gets pretty dry between rains the water would be used for in between. I could use several smaller containers to store that excess water (if there was any). Is there a video or a visual that would be helpful? A term to google? I have searched but these days the net is full of irrelevant and similar info.

Hi
my climate ,rainfall is much different but would probably still work for you depending on evaporation.?? I run my downspouts ,underground into a water garden . Provides storage for the water ,
filters the pool and overflow goes into a marsh garden . Allows about 2000 gallons of water storage and is not a gigantic eyesore lol
I have a fountain in one which has bypass plumbing allowing the water to be used for individual plants or can dip out water as needed. . Was originally built to hold rainwater but became a water garden, fish pond Has worked well for over 20 years .
Works for me anyway gary