Is it a religious obligation to pay the state for water if it does not mandatorily demand it, and what is the ruling on consuming water in past years without payment?

If paying water bills is optional in this area, meaning the concerned authority has permitted the use of water without demanding payment for it, then this is considered permission and allowance. You are not obliged to pay anything unless you volunteer. Customary permission takes the place of actual permission, and where permission for free use exists, the user is not obliged to pay for the water.