Harmless Geosmin in Omori water supply

FAQs – Geosmin

If your water smells or tastes earthy, musty, mouldy or dirty, you are highly likely smelling/tasting geosmin. Here are some answers to common questions we're hearing:

Is my water safe to use and drink?

Yes, your water is safe. When Taupō District Council receives a new taste and odour complaint we arrange for water sampling as soon as possible. We test for a range of things that can cause taste and odour and check for treatment plant operational issues or network issues. We also check all our routine monitoring information and water quality data.

All taste and odour testing undertaken to date has revealed the intermittent presence of geosmin in some water supplies, particularly in the Omori water supply.

Any concerns that water is unsafe are taken very seriously. We will respond urgently and ensure the community are well aware of any issues. An alternative water source would be made available as soon as possible if we cannot guarantee the safety of water.

What is geosmin?

Geosmin is a naturally occurring chemical produced during the breakdown of algae and other micro-organisms in raw (untreated) water sources. It is also present in some foods such as beetroot and mushrooms. It has a distinct earthy or musty odour which most people can easily smell and causes most taste and odour outbreaks in drinking water. Seasonal increases in naturally occurring algae or bacteria in water can cause geosmin levels to increase above the tasting threshold.

Geosmin can be detected through taste/smell at incredibly low concentrations. Most people can detect geosmin at around 15 parts per trillion (ppt). A sensitive person may detect geosmin as low as 5 ppt – that is about 1 teaspoon in 200 Olympic sized swimming pools! At Omori, we have measured geosmin around 15 to 25 ppt.

Why is geosmin present in our water supply?

Your water is sourced from Lake Taupō. All surface water is susceptible to algae growth and contains a mixture of microorganisms. Our water treatment plant is currently unable to remove the chemical geosmin.

My water usually tastes and smells fine, why is it so bad now?

Algae and microorganism growth is variable throughout the year, so geosmin presence will be variable too. Taste and odour issues usually occur when water temperatures increase. The presence of organic matter in a water supply may also be affected by rainfall, runoff and lake levels. Spring and summer 2022/23 have been particularly unsettled with high rainfall which can wash sediments containing organic matter into the lake.

How long will the taste and odour last?

It is difficult to predict how long the issue will last as it is dependent on environmental conditions. Geosmin levels will vary throughout the year.

How do you know it’s geosmin? It might be something else

We are periodically testing to confirm geosmin remains in the water and is the cause of the taste and odour. The suite of tests we do includes other taste and odour compounds as well. We also have a comprehensive list of routine water quality testing that is ongoing.

What is TDC doing to improve this issue?

Short term

• TDC will continue to flush water in the network when the issue flares up. This will prevent a build up of sediment, organics and stagnant water in the network. You may occasionally see Downer, TDC’s three waters contractor, on the road side flushing at times when the issue is noticeable.
• Water quality monitoring continues to ensure water is safe. We monitor key water quality parameters at up to one minute frequencies and our operations team are on call 24/7 if water quality goes outside our target values. We also sample in the network every week and test for bacteria and other parameters. You may see Eurofins, our sampling contractor, out and about sampling and testing water in the community.
• Our monitoring programmes are set up to comply with the Drinking Water Standard for New Zealand. Our sample scheduling, test methods and response procedures align with the standard. Any issues we have, including taste and odour, are forwarded to Taumata Arowai, the water services regulator for NZ.

Long term

• A substantial upgrade of the Omori Water Treatment Plant (WTP) is under way. The new WTP will include a membrane filtration process as well as arsenic removal (arsenic is a geothermal chemical that is naturally occurring in Lake Taupō). The new WTP will remove organic material and therefore the source of geosmin.
• You will see physical works on this project start this year (2023). TDC will be providing updates to the Omori, Kurutau/Pukawa communities as this project progresses.

Is there anything else I can do to improve this issue?

You could try chilling your water, adding ice cubes or a few drops of lemon juice. If you have been away from home for a period, ensure your house plumbing is well flushed.

Now we know what the issue is, should I tell TDC if it comes back?

Yes. It is helpful to know when the issue comes back or gets worse. Or if you need reassurance that we are keeping a watch on water quality. Geosmin may be intermittent in a water supply and present in variable concentrations. If it goes away and comes back it is good to know so we can arrange another test and double check that it is still geosmin causing the problem, not a different issue.

Call the customer service team on 0800 ASK TDC or email info@taupo.govt.nz so we can log it in our system and take any actions we think will help.