I have one floor mall with 10 shops (4 meter height), I should supply water from the main drain (3 inch) connected with pressure reducer (1 1/2 inch). I don't have the flow rate of at the 1 1/2 inch, but i know that the water can reach the roof. I am planning to install 3 plastic water tanks with volume of (3000 litre each).I was thinking to connect those three tanks with valve. The owner insist to have for each shop different centrifugal pump with 1 1/2 inch pipe. Is't acceptable and workable to provide 10 small pumps (divided into 3 groups, 4 pumps connected to the first WT, 3 PUMPS TO THE SECOND AND 3 FOR THE LAST WT). please advise if that feasible and what should be the best solution in this case. thanks in advance
In the beginning you mention supplying water from the main drain, but I'm assuming you mean meter. From there, you go to a "pressure reducer". You may have a pressure reducer, but given that you are cutting the pipe diameter in half, can you please clarify if it is actually a pressure reducing valve or if you just mean a pipe reducer (will make the pipe sizer smaller).
I wrote an entire answer before I re-read your question and realized you were not asking about 3 pumps vs 10, but, simply, if 10 pumps would work. First of all, if this is for a commercial application, I think that you should have a plumber or engineer probably designing the system since there is more than just throwing some tanks on a roof and hooking up pipe involved here. There are some different isolation valves and other items--like strainer(s)-- that should probably be installed. With that being said, I think having 10 small pumps in this application sounds like an overcomplication. If you are connecting the 3 tanks together (you say valve, but I think you mean manifold), then you really only need one pipe outlet from the collective tanks. Then you can run the pipe throughout the mall to the various shops. Depending on the distance to the furthest run, you will probably need pressure reducing valves for the shops (particularly those close to the pump). You could also put two pumps by the tanks in parallel to provide a level of redundancy if one pump fails, as well as additional capacity if there is a high demand on occasion. 1 1/2 inch pipe suggests there may be either reasonable demand or the owner was just throwing a number out there.
Hopefully that answer is enough for you to get started or at least enough to figure out what other questions to ask. If this is a real project and not just a design exercise, I highly encourage you run it by a licensed professional, and, as Solar Mike said, make sure you heed the local codes and regulations being enforced. Water systems won't explode when poorly designed (which is a possibility with natural gas), but you can cause severe property damage if there are failures or leaks, and you can make people sick if you have things like large sections that are never used which will sit with stagnant water in the pipes until someone eventually turns on a faucet.