Eco-friendly laundry balls and soap nuts have been put to the test - and the results are hardly better than using plain tap water.

Consumer New Zealand has revealed the dirty truth about the alternative washing solutions, testing four laundry balls and one soap nut brand against everyday stains such as grime, grass, make-up and baby food.

But people would be better off using water, Consumer NZ head of testing Paul Smith said.

"You achieve similar results to laundry balls or soap nuts but it won't cost you a cent," he said.

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Laundry balls are made of plastic or rubber and usually contain mineral pellets, while soap nuts are made of tree nut shells which are put inside a bag to wash with your clothes.

The products claim to be eco-friendly and able to be used for up to 1000 loads of washing.

The laundry balls tested by Consumer NZ were made by Eco Zone, Live Simply, Miracle II and Sheer Wellness - with some of the products costing $120 a pop.

Two of the solutions - Eco Zone Eco Balls and Live Simply Laundry Ball - performed slightly better in the tests but the difference was hardly worth noting, Consumer NZ's Sue Chetwin said.

Claims made by the laundry ball manufacturers were also a concern, she said.

Miracle II said its sealed rubber laundry ball was filled with "Miracle II soap and neutraliser" and emitted "a strong negative ion field and breaks up water molecules so they can reach further into fabric and clean better".

One of the companies said its laundry ball could also be used as a massage ball - a better suited purpose, Ms Chetwin said.

"You'd be better off saving your money and just using water to do your laundry," she said.

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"The claims they make to encourage people to think in some way they will be washing well and that they will be environmentally friendly, which is pretty much rubbish. It's the sort of claims that try and seduce people with using odd words and they try and sound scientific."

The soap nuts, shells of tree nuts containing saponin which users put inside a bag to wash with their clothes, also performed poorly, she said.

None of the products performed anywhere near as well as Persil powder, which they were tested against, and was a Consumer NZ recommended product.

The tests were carried out on cold water cycles in a front-loading machine.