A water meter at a residential property. Photograph: Andy Mabbett / Wikicommons

Councillors are seeking assurances from Thames Water that residents unable to have water meters fitted in their properties will not be financially “disadvantaged”.

Thames’ plan to start billing residents directly from 1 April rather than through the council has caused heated debate at the Town Hall in recent months.

The borough’s housing scrutiny committee is now going over the details of the changes, with Cllr Gary Heather pointing out that those unable to secure a water meter, which records the amount used in a home for billing purposes, could be worse off.

According to Thames, properties with complex plumbing, particularly those living in flats, means that it is “not always possible” to install meters. These residents are instead charged through a tariff based on the average water use in similar properties.

Cllr Heather said: “It’s alright them having a special tariff, but how would that compare if they could have a water meter? 

“People should not be disadvantaged because the technical solution from Thames Water is not possible. 

“Let’s spell it out – they should not be disadvantaged by not being able to have a water meter fitted.”

The company says it offers a cheaper tariff for single occupant households, and promised that if a resident’s current rate is cheaper than the tariff following an assessment, they will stay on that rate.

This arrangement is available only to those who have applied for a meter but have been unable to have one fitted, “either because it’s not possible or it would be too complicated to fit”.

Council officers confirmed that low water users and single occupants are the ones “losing out”, with committee members pressing for an answer on how many households in Islington are unable to have water meters.

Cllr Phil Graham said: “You can’t solely base your water use on the amount of people in a building. One person can use more water than two. Seeing as we have not had water meters before, how can you work out whether they are high or low user?”

To further complicate the situation, councillors were told that while many can save money by having a meter, larger households or those with medical conditions that mean they do a lot of laundry can actually be better off without one.

All tenants living in council or housing association properties will be billed directly by Thames from 1 April.

In a statement on the changes, Islington Council said: “Thames Water no longer uses external organisations such as councils to collect the water and wastewater charges. They have worked with other councils to make this change and Islington is one of the last boroughs to carry out these changes.

“There is no option to opt out of these changes as we will no longer have an agreement with Thames Water to collect payments on their behalf.”

Meters are being compulsorily installed, where possible, across Thames’ whole supply area.

According to the company, residents can compare bills for a year with the option to switch to a metered bill at any point if they see it would save them money.

Those who find their bills go up will have a year before they start paying for exactly how much water they use, with Thames adding: “This is done so customers aren’t shocked when they first switch to their metered bill.”

A spokesperson for the company said: “We’ve been working closely with Islington throughout the transition period to Thames Water billing and will continue to do so.

“We have a range of alternative tariffs and financial support options for customers to make sure no one is disadvantaged and we’re talking with local residents’ groups to discuss any concerns they have.”

If you are struggling to pay bills, you can visit fuel poverty referral network and free energy advice service SHINE by emailing shine@islington.gov.uk or calling 0300 555 0195, or access Thames Water’s Water Help scheme.

You can also get free, confidential and independent advice from Citizens Advice Islington on paying bills, rent and mortgage by calling free advice line 0808 278 7836, Monday to Friday between 10am and 4pm.