A permanent solution to Katherine's water supply woes may take up to two years, as residents continue to endure water restrictions put in place when PFAS chemicals were discovered in the Top End town.

The restrictions were introduced in August 2017 after the chemicals, which are linked with potentially toxic firefighting foams, were found in the town's bore water.

Authorities say the town's water supply remains safe to drink, and the restrictions were designed to limit the amount of contaminated bore water used to boost supplies during the dry season.

Katherine's water supply is a mix of river and bore water, and during periods of low rain — such as the dry season — more water from the town's bores must be used.

Water services general manager Rob Brito told ABC Darwin the measures would be lifted when a new water source for the town was established.

If you live in Katherine: Odd-numbered properties are permitted to irrigate Monday, Wednesday and Saturday from 6:00pm to 8:00am

Odd-numbered properties are permitted to irrigate Monday, Wednesday and Saturday from 6:00pm to 8:00am Even-numbered properties are permitted to irrigate Tuesday, Thursday and Sunday from 6:00pm to 8:00am

Even-numbered properties are permitted to irrigate Tuesday, Thursday and Sunday from 6:00pm to 8:00am No watering of hard surfaces

No watering of hard surfaces Hand-held watering via a bucket or watering can is permitted at anytime Restrictions are in place from August 21 and will be reviewed in November.

The options include a new bore field on the northern side of the Katherine River and an expanded treatment plant for groundwater sources.

The current treatment plant was supplied by Defence to remove PFAS from Katherine's groundwater and has been in operation since October.

But it only treats up to 1 million litres of water a day.

Power and Water are also looking at an alternative source of water as another option, but there may be risks PFAS could be drawn up in the future.

"We've looked at alternative groundwater sources, at a different, a number of locations," Mr Brito said.

"There are risks that any groundwater source today may be not have any PFAS whatsoever, but a few years down the track you may end up detecting or drawing through PFAS.

"Hence we believe a treatment solution provides certainty now and into the future."

An expansion of [the] treatment plant, as a permanent solution, could take 18 months to two years to be completed, Mr Brito said.

"Providing a new safe water source to a community is complex," Mr Brito said.

"We absolutely want to get the right solution in place, and we want to get the right solution at the right time."

Katherine's water supply is a mix of river and bore water. ( ABC News: Sally Brooks )

The water-saving measures include only watering lawns with a sprinkler three days a week, and not watering hard surfaces.

Per-and poly-fluoroalkyl substances, also known as PFAS chemicals, are a group of chemicals that were commonly used in firefighting foam, and are being investigated by Australian and international health authorities.

The chemicals were used at the Tindal RAAF base in the late 1990s and early 2000s as part of firefighting operations.

About 50 properties near the Tindal RAAF base are already receiving bottled water supplies, as a precaution, and have been offered rain tanks.

It is believed Katherine is the only town in Australia to be put on water restrictions due to PFAS contamination.

Dry season prompts water use to soar

Mr Brito said water usage in Katherine had risen significantly over the past two weeks as the dry season approached and temperatures soared.

"As we've slowly entered the dry season, demand has increased in the last two or three weeks, which is the reason for the timing to remind people that we need your support in conserving water," Mr Brito said.

Katherine residents were offered blood testing following the release of an interim human health risk assessment by Defence which warned against eating local seafood and home-grown produce.

The voluntary blood tests are on offer for people who live or work, or have lived or worked, in the RAAF Base Tindal investigation area.

The tests are available from March 17, 2018 to April 30, 2019.