What you put in the lease is what you have to abide by. If you wrote in the lease that the tenants do not have to pay for water, then they do not have to pay for water.
It is your responsibility. In your next lease you should safeguard yourself better so that if there is another bill that you presumed will be covered by the HOA then you will need to write it in the lease that if the HOA fails to cover that payment, then it will be the tenants responsibility.
It is not fair for you as a landlord to impose fees upon the tenants that you did not agree to in writing and identify in the lease.
