I rent a commercial building from a plumber.The water heater broke and flood our side and the landlords side.Who is responsible?

Usually commercial leases requiee the tenant to be responsible for maintenance and repair, unless the defect affects the whole building, like an air conditioner outage. You need to check the language in your lease and see what it says about this type of repair, or hire a lawyer for help. Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.