Water filter company HRV has pleaded guilty to 11 charges laid by the Commerce Commission related to false and misleading claims about the benefits of its filters and the quality of New Zealand's water supply.

Charges were laid in Auckland District Court on Monday under the Fair Trading Act, and related to claims HRV made between July 2014 and October 2017 on its website and through promotional content.

The commission said HRV's claims about its filters' water-softening properties and ability to reduce skin conditions such as eczema and dermatitis were unfounded.

HRV also misled consumers about the levels of chemicals and additives in New Zealand's domestic water supply, and the need for consumers to buy a water filter to address this.

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In a statement HRV said it had removed any inaccurate information based on the commission's investigation and promised tighter control over its marketing material in the future.

Hard water is the term used to describe water containing high levels of minerals. When water contains high levels of minerals, it tends to deposit these minerals onto surfaces - often referred to as "scale".

Hard water can also make soap form a scum on surfaces.

Conventional methods of treating hard water (reverse osmosis and ion exchange) involve removing the minerals from water which cause it to be hard. The result is soft water, which does not cause scale or scum build up.

HRV will be sentenced in September.