Constructing sump in old building

[alpssolomon]

Hello All,
I purchased a house recently and the previous owner built the house without water storage sump since the yield from the borewell was good. The pump auto-pumps the water to the overhead 4000 Ltr tank and hence the two-storey house is self-sufficient regarding the water is concerned. The street has not yet received cauvery connection yet. But I want to be prepared for the cauvery water connection or in the event of the borewell going dry etc. Hence i am looking for an Engineer/Contractor who can study, advise and implement construction of water storage sump. I shall be grateful for any credible lead from you.
Thank you
Solomon