This week, the Herald on Sunday raised the matter with Watercare which agreed to take another look at its invoices.
The Watercare charges are currently itemised as volumetric and fixed charges on the paperwork - but there's no clarification about who should pay.
Evans said there were cases where landlords have even tried passing on their entire rates bills to tenants."It's not common, but some landlords try their luck."
Julia Hart, co-ordinator of North Harbour Budgeting Services, said the extra cost can mean the difference between tenants being able to take their child to a doctor or not.
Her advisers check their clients aren't paying the landlords' component of the bill, but she suspects landlords are unaware of the rules rather than acting deliberately. Hart agrees it needs to be clarified for both parties.
This week, a Watercare spokeswoman said it would consider clarifying the responsibilities on the 390,000 invoices sent to residential customers each month. "This is definitely something we will look at doing. We are planning a system upgrade which will provide greater flexibility in the future."
The spokeswoman confirmed there had already been queries about the charges since monthly invoicing began a year ago.
The Citizens Advice Bureau said it had fielded 140 inquiries in the past year - most from people confused about who should pay.
An estimated 20 per cent of the 120,000 rental properties in Auckland are managed by rental agencies, which appear to be in the clear as most bill landlords and the tenants separately for appropriate charges.
The Ministry of Business, Innovation and Employment says the annual fixed water charge is imposed whether the property is occupied or not, and is therefore the responsibility of the landlord.
All other water use charges would usually be tenants' responsibility. The ministry advises tenants who have paid the fixed charge to ask for their money back.