Perhaps something along these lines:
Addressing the Letter
Your letter should be addressed to the Secretary of the society and a copy to the Chairman (or equivalent).
Sample Letter
Dear [Recipient's Name],
It is with regret that I once again write to you regarding a serious water leakage problem.
Provide details of what happened and relevant dates if the complaint relates to more than one incident. If you have detailed information, it is best to summarize your complaint and include these as enclosures, such as previous letters. Make it clear what you want to achieve as an outcome.
Concluding the Letter
You may wish to conclude the letter in the following style:
I would appreciate it if you could carry out a full investigation as to the cause of the leakage and take all necessary steps to correct the problem. May I remind you that water is a very scarce resource and any leakages only add to this scarcity; therefore, it is imperative that urgent action be taken.
I am sure there are other members of the society who face a similar problem; therefore, I would further appreciate a full response to this letter in accordance with the society's complaints procedure and stated timescales (if any).
Yours Sincerely,
I hope the above helps.
Regards,
Harsh