Generally you cannot offset maintenance/repair costs you have incurred against your rent. In fact, you generally cannot offset anything against your rent. It is possible, although extremely unlikely, that your lease (if you have a written one) covers this scenario. If it does, the provisions of the lease will control. If it does not, you cannot deduct any repair/maintenance costs you incur from your rent. Find your lease, and then if you think its necessary find a local landlord/tenant attorney.
Necessary Disclaimer: Not intended as legal advice. Do not take any action or fail to take any action in reliance on the above.
Generally, landlords are required to maintain plumbing in good and safe working order. Your lease may contain language about repairs, but you should contact a landlord/tenant attorney in your area and bring a copy of your lease for his/her review. You can also contact local housing officials if you believe the landlord is violating any of his/her legal obligations. Good luck.
DISCLAIMER: This response is made available for general educational purposes only, and not to provide legal advice upon which you should rely. Mr. Kam does not give legal advice without a full and complete understanding of the facts and circumstances of a given situation -- of which the question and answer format provided for herein does not qualify. By viewing this response you understand and agree that: (i) no attorney-client relationship has been formed between you and Mr. Kam or his law firm; (ii) you will not rely on any statements or opinions provided in this response; and (iii) this response shall not be used as a substitute for obtaining legal advice from a licensed attorney in your jurisdiction after a thorough consultation.