Discoloured water

What we're doing to minimise discoloured water in the city, and what to do if your water is discoloured.

Palmerston North residents sometimes experience discoloured water coming out of taps. This is for two reasons:

  • We have slightly high levels of iron and manganese in our water
  • Pipes that carry the water tend to develop a small layer of biofilm over time. The biofilm can trap some of the iron and manganese, which can occasionally be released and cause discolouration.

My water is dirty. What do I do?

Leave the cold tap running for 20 minutes to see if the water runs clear. If not then call us on 06 356 8199 and we will flush the pipes around your property. The discoloured water may stain clothes, so we advise postponing doing the laundry until the water is clear again.

Find out about why you might see cloudy water running from your taps, and how you can solve it.

If you've ever noticed a cloudy or white appearance in your tap water, don't be alarmed. This is common in many water supply networks and caused by tiny air bubbles in the water.

These bubbles form due to fluctuating pressures and flow rates in the pipes below the ground. When water is under high pressure in these pipes, air dissolves into it. Once you open the tap, the pressure drops, and the air comes out by appearing as tiny bubbles. Within a minute or two, these bubbles are released and your water clears up.

The cloudy appearance is not due to any additional chemicals in the water supply.

We only add chlorine and fluoride as required by national regulations and the Ministry of Health. We constantly monitor these levels to ensure the best possible safe drinking water for our everyone in our community.

Water supply routes and flow rates change constantly due to varying demands for water in different areas.

Additionally, routine and reactive maintenance, such as shutting valves or pipelines, can alter the flow of water through the pipes, leading to temporary changes in water appearance. That’s why your water may appear clear most of the time and only occasionally appear cloudy.

Cleaning the main water pipes

Every year we clean the two main water supply pipes that gets water from Turitea Dam to Palmy homes and businesses, to ensure our city's water stays safe and pristine. This process is called swabbing and usually happens in winter because we need to do it when the Manawatū River is in high flow.

We do this because the water from the dam has relatively high levels of dissolved iron and manganese. We remove most of this during the treatment process but over time the minimal remaining amounts can build up in the pipes. While this doesn’t affect the safety of the drinking water, it can cause it to become discoloured. Cleaning the pipes ensures this isn’t a problem.

The cleaning is done late at night when less water is being used. 

Flushing of all water mains within the city is performed on a rotating yearly schedule, usually in August. The 2 water mains supplying the city are flushed in alternating years. The pipes were last cleaned in August 2024.

We're also replacing old pipes in the water main network with plastic ones. 

Can I still use water while the pipes are being cleaned?

Yes, the water remains safe to drink, so you can still use water while we clean the pipes. We do this work at night so fewer people are using water. Try not to do your washing overnight though, as your clothes may be stained if the water is discoloured.

Some residents in Turitea won’t be able to use water, but those homes will have received a letter from Council.

How do you clean the pipes?

We start by shutting off certain valves (or taps) to the main pipe. This causes the water to be stuck behind these taps. We insert a giant sponge into the pipe. Then we open those doors and the pressure of the water pushes the sponge through the pipes. As it moves through the pipes it cleans them. Near the river, we remove the sponge so it doesn’t end up in our precious awa. The water and any sediment or biofilm is then flushed into the Manawatū River. Our consent conditions have very strict rules about when we can do this work to ensure the effects on our river are as minimal as possible.

Why does our water have manganese in it?

The water that goes through these pipes comes from our Turitea Dam, or from various bores across the city. Manganese is a mineral that naturally occurs in rocks and soil. We remove almost all of it during the treatment process, but tiny amounts are dissolved and still get through. Over time that can build up in the pipes. We remove it to ensure the city’s water supply isn’t discoloured.

The Ministry of Health has a health guide of manganese of less than 0.4mg/L. Palmerston North’s is typically 0.01mg/L, and we test it frequently.

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