The landlord has the obligation to provide rental premises that are "fit for  their intended purpose," and providing safe drinking water is part of that obligation. Failure to do so violates the "implied warranty of habitability." When this warranty is violated, the tenant may be able to sue for monetary compensation; take action to correct the problem him/herself and deduct the cost thereof from the rent; seek a court order directing the landlord to fix the problem; and/or terminate the tenancy and move out without penalty.Exactly what you can do depends on the exact circumstances, including whether you have provided the landlord notice of the problem and a reasonable chance to fix it. You should consult with a landlord-tenant attorney about the situation and the remedies available to you.