The rental agreement will govern what the landlord may, or may not, pass through as expenses to the tenants. Ideally, the rental agreement would state that a tenant is allowed to view a copy of the bill at the rental office, or provided a copy, whenever there was an adjustment. Unless someone is taking a constant shower, or cannot get away from the toilet, on a continuing monthly basis, that's an awful lot to charge. Certainly does seem very suspicious. In the absence of a written lease, or the written lease stating a right to see the water bill, I think the general requirement of dealing in good faith implies that the landlord should produce the water bill.
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