Much of the world's tap water contains little bits of plastic, a study has found.

Contamination has been found worldwide, but Auckland tap water is not currently tested for microplastics.

The city's supplier Watercare said its water was filtered and safe to drink but it was "proactively investigating" how to test for the small particles and fibres.

Current methods varied internationally and were not "completely reliable", Watercare water supply manager Priyan Perera​ said.

FRED DOTT/GREENPEACE Larger bits of microplastic.

International research, reported by theguardian.com, has found microplastic contamination in much of the world's tap water.

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The investigation by Orb Media found 83 per cent of samples contained plastic fibres. In the United States, 94 per cent of samples were found to be contaminated.

SIMON SMITH/STUFF Watercare's Priyan Perera says Auckland's drinking water is "Aa" graded.

Normally, between 8 and 15 per cent of Auckland's tap water was taken from the Waikato River, downstream from the city of Hamilton and wastewater treatment plants.

Perera said Watercare filtered the water before it was piped to Auckland at its Waikato Water Treatment Plant, including with membrane ultrafiltration technology.

"Based on current understanding, membrane ultrafiltration is the most effective routinely employed treatment barrier to microplastics. This will be confirmed once a testing protocol has been confirmed and implemented."

DOMINICO ZAPATA/STUFF The city of Hamilton is up river of where Auckland takes some of its water for drinking.

Dams in the Waitākere and Hunua ranges provided most of the city's tap water and this was filtered down to 4 micrometres in size.

Perera said that although microplastics could be smaller than this, the dam water was of "extremely high quality" and came from protected catchments with "little if any human influence".

​Dr Trisia Farrelly co-founded the New Zealand Product Stewardship Council, and specialised in research on plastic waste.

123RF People should think about how they wash garments with microfibres, scientists say.

She said it was reassuring Watercare was investigating microplastics in drinking water and that it was working out how to test for them.

"It is essential that our municipal authorities are proactive in this regard as microfibres are the worst microplastic offenders when it comes to environmental and human health."

Farrelly said international reports suggested microfibres could be too small to be removed by sewage treatment plants. Those fibres were now present in most fish tested in New Zealand, she said.

WATERCARE Watercare's Waikato Water Treatment Plant in Tuakau.

"Plastic microfibres leach endocrine-disrupting chemicals and carry persistent organic pollutants in increasing concentrations up through our food chain."

Professor Mary Sewell of Auckland University has researched microbeads in facial cleansers and shown the plastic had a good chance of making it from the bathroom sink to the ocean.

The Government was to ban such products next year.

WATERCARE Watercare's Waikato Water Treatment Plant in Tuakau.

But there were other ways microplastics got into waterways and fish, she said.

This included larger plastic items, such as drink bottles, that broke down over time.

A study had also shown that polyester fleece clothing released 3000 to 4000 microfibres down the drain when washed.

Sewell said the science on microplastics in the environment was "gradually becoming much more solid", and people were starting to realise its potential implications.

"The ubiquitous nature of this as a problem is becoming much more apparent."

European research this month found that most sea salt contained microplastics, Sewell said.

"If we ... have salt on our fish and chips, then we are getting plastic from our fish, and plastic from the salt as well."

HOW TO REDUCE MICROPLASTIC IN WATERWAYS AND OCEANS

Dr Trisia Farrelly said people should lobby the government and manufacturers of dryers and washing machines to do something about it.

People could also:

* wash synthetic clothing less often and wear garments less likely to shed fibres

* wash clothes in full loads with liquid laundry soap and cold water, and spin dry at a lower speed to make it less likely fibres will be sloughed off

* put lint from the dryer in the bin, not down the drain

* buy washing bags and washing machine lint filters designed to capture fibres

* refuse single-use plastics.