Is providing DG backup service is taxable, for multiple tenants in a one building? we are a facility mgmt comp?

Is providing DG backup service is taxable, for multiple tenants in a one building? we are a facility management company, providing services as part of our business. The building owner owns the DG-set we buy the fuel for it to run, at the end of the month we collect the money back from the occupants for whatever we spent during the period to which we have to provide the bills.