No. You bought the house, presumably knowing that there was only one water line and one meter for both houses. This was something you should have addressed as part of your purchase contract. You are probably stuck with the status quo unless you want to spend more on litigation than you would spend on a new meter and water line.
Nope. Perfectly legal. No law against it. It's not even a civil wrong. You agreed on a 50/50 split without taking into consideration who uses what. That's a contract. To modify the contract you need the agreement of both owners.
Let's put this into perspective.
How much is the water bill each month? Give me a dollar amount. If it varies, give me the monthly average.
In whose name is the water account?

