Laundry balls are no better at getting clothes clean than washing in plain water, Consumer NZ says.

The balls sell for more than $100 each and manufacturers claim they can be used for hundreds of washes.

But the watchdog said its testing showed consumers were wasting their money.

Four laundry balls and soap nuts were tested by Consumer NZ.

A spectrophotometer was used to analyse how well each product removed some typical stains, including everyday grime, grass and mud, chocolate ice cream, make-up and baby food.

The tests showed two of the laundry balls, Miracle II and Share Wellness, consistently delivered the same or a poorer washing outcome than washing with plain water.

Another two, Ecozone and Live Simply, performed only slightly better.

Soap nuts were less effective than water for everything except tomato and baby food.

Consumer NZ head of testing Paul Smith said people who preferred to avoid regular detergents would be better off not using anything. "You achieve similar results to laundry balls or soap nuts but it won't cost you a cent," he said.

He said some claims for laundry balls were wacky.

One website claims the Miracle II Laundry Ball is "eloptically energised" and "emits a strong negative-ion field and breaks up water molecules so they can reach further into fabric and clean better".

Smith said: "If those claims don't ring alarm bells, its price should. At $119 for a single ball, you'd expect it to work miracles but our test found it didn't have any special dirt-removal powers."

Consumer NZ chief executive Sue Chetwin said the tests were done according to the manufacturer recommendations, with a cold wash in a front-loader machine.

She said the manufacturers seemed to be trying to blind people with false science.

"People think they are doing something good for the environment and also getting their clothes clean but they would be better using water. They all performed badly."