False commitment by builder how to take action and raise complaint?

Dear Sir,i have bought the apartment in Chennai, Perumbakkam with reputed builders, While booking the sales team have promised that ground have good enough potable water to drink and all other purpose later on after construction and reach certain stage we came to know that we don't enough water provision to live and also no provision from corporations. we forcibly requested Builders to about stand, they conveyed us we have tried different way through bore well but water in not potable drink or any other purpose. After we formed volunteer team, we have did R&D and find the solution to install RO plant overcome the situations. The builders initially agreed to proceed further they said we don't issues intern of money, after several follow up with builders, They agreed to share 50% remaining 50% they tossed on owners side.We are owners have to move forward to achieve 100% builders for their ignorance. requesting your advice.