Confusion over who is responsible for fixed water charges could be costing tenants hundreds of dollars annually.
The Residential Tenancies Act says it is the landlord's responsibility to pay for the fixed water charge while tenants are responsible for paying the water they use.
But many appear to be unaware of the rule.
The Tenancy Tribunal ordered landlords to pay out $10,242.20 in fixed water charges across 25 cases in 2015 and 2016 - and it's still happening now.
Sacha Green, national legal advisor for Citizens Advice Bureau, says the issue stems from "a lack of understanding".
She told Newshub over the past few months she's seen tenants paying for all kinds of things they're not liable for, including fixed water charges.
"The landlord is responsible for paying for bills that must be paid whether or not a tenant is living there. With fixed water charges, these are costs incurred regardless of whether or not the property is occupied by tenants so the landlord is responsible for these."
She says tenants should always carefully read tenancy agreements to see what it says about water bills - but regardless of what it reads, they should be aware fixed water charges are always the responsibility of the landlord.
"The tenant is responsible for paying for the water they use, which means there has to be a separate water meter that measures the usage only for that property," said Green.
"If there isn't a separate water meter for the property, the landlord is liable to pay for all the water charges."
Green says some tenants have been asked to pay charges without evidence of a bill - which is another thing to be wary of.
Under the Residential Tenancies Act landlords must keep copies of all documents relating to their rental during the tenancy and for one year after it ends. These can be requested by the Ministry of Business Innovation and Employment.
If you suspect you're being overcharged, ask your landlord for a copy of your water bill which will make your charges clear.