I think that from the past three month the water charges is increasing that need to be controlled, Kindly also observe the people who are staying at your half duplex whether they are using some or more water as needed. Also check water bills with water department for cross verifying whether landlord is saying correct information or not..

If you are facing more problem with Landlord go ahead with RPA for further action on same. https://www.rentalprotectionagency.com/complaint_center_form.php