Safe H2O

How Often Should I Clean My Water Tank in New Zealand?

If you are one of the thousands of New Zealanders with water tanks on your property, you will want to know how often you should clean your water tank.

Here in NZ the Ministry of Health recommends you should clean your water tank once a year.

If your water source is rainwater off the roof then you will get bacteria in your tank water at different times.  

This is inevitable due to bird droppings, amongst other things, carrying bacteria such as E-coli right into your tank.  The same risks apply if your water source is a stream/surface water and often this applies for a shallow bore.  

The key is to minimise the amount of sediment in the bottom of the tank as this can provide a breeding ground for bacteria to grow and thrive in.  

The other problem with sediment in your tank is that it can minimise the effectiveness of UV treatment by blocking the UV light from reaching the bacteria.  

This in turn increases the health risk.

Related: How much does it cost to clean your water tank?

For rainfed tanks factors to consider when you determine how often you get your tank cleaned are:

  1. What is likely to get in your tank?  How many trees do you have surrounding your property and leaves getting on the roof, are there busy roads and/or unsealed roads nearby causing dust, likelihood of spray drift (pesticides and fertilisers) from surrounding agricultural and horticultural activity, and how much pollen do you get at the property?
  2. Who is using the water?  Younger and older people are more at risk should anything go wrong with your water, as is anyone with an underlying health condition.  Visitors would also be more at risk.

In the end it comes down to personal choice about how particular you want to be about the quality of your water for you and your family. 

A regular cleaning regime to keep on top of the risk is advisable and from experience of looking at thousands of tanks we recommend you should clean your tank at least every two years.

What can I do to ensure clean and safe water and minimise my risks?
Before the tank

Keeping your roof and gutters clean helps minimise the amount of sediment getting into your tank(s). In the right circumstances leaf diverters can also help prevent the organic matter that enters the tank.

The same applies for leaf guards and bristles. Having a flushing cap and regularly opening this after rain events is also a simple and effective way of reducing the amount of organic material entering the tank.

There are also first flush diverters of varying designs that perform a similar function.

At the tank
Nothing will fully stop all sediment getting into your tank so regular tank cleaning is a must.
You could also consider a floating out-take pipe so that you are drawing the water from your tank well above any sediment that may collect at the bottom of the tank.
This is less of a factor if you undertake regular tank cleans!
If you have more than one tank and they are equalised (joined) then the primary (first recipient of water off the roof) tank will gather a greater amount of sediment in it than the subsequent tanks.
In this circumstance drawing your water into the house from the secondary tank(s) is sensible.
After the tank
Some form of filtration at your pump is advisable to provide ongoing protection between tank cleans, as the sediment present in the tank water builds up again after a tank clean. This works ‘hand in glove’ with a regular tank clean to provide safe and clean water. See below for more about filtration.
What if I don’t clean it often enough?
Without regular cleaning of your tank the sediment in your tank will build up and increase the health risk to you and your family.

It does this by providing a medium in which bacteria that enters the tank can thrive. Further, it is more likely to minimise the effectiveness of any filtration you have in place.

As sediment goes into solution in your water, it can overwork your filters (meaning you are having to change filters before their expected lifespan) and can render UV systems less effective by blocking the light from reaching their target of bacteria in the water.

To reiterate, regular tank cleans go hand in glove with filtration. Either tank cleaning or filtration by themselves are an improvement on doing nothing, but do not provide the level of protection that both working together do.

Does my location make a difference?

In short, yes, location does make a difference in terms of how quickly sediment builds up in your water tank.
Factors to consider are how many trees overhang or surround the roof of your property, how close you are to roads and how busy they are (especially if the road is not sealed), how much pollen is blown across your property, what is the risk of spray drift from surrounding agricultural and horticultural activities, how close are you to a beach for windblown sand.
Signs that indicate the water tank needs cleaning

Signs that indicate a water tank needs cleaning include but are not limited to:

  • Smell to your water
  • Taste(s) in your water
  • Colour in your water
  • Looking in your tank and seeing sediment on the bottom
  • Filters blocking before their expected lifespan and/or being highly discoloured in a short period of time
  • Loss of water pressure in the house
  • Ongoing tummy upsets and other ill-health in the household, especially if it clears when you are away from home


Read more about the typical signs that your water tank needs a clean.

These indicators tend to occur when the tank is overdue for a clean.  The best approach is to arrange a regular clean every 1 to 2 years as part of your ongoing maintenance regime.  

Doing this means you are far less likely to experience the above symptoms and are minimising your risk on an ongoing basis. 

Do I need to replace the water?

With the traditional tank cleaning method of emptying the tank, mucking it out and then refilling it, the answer is yes.  However, the Safe H2O process treats both your water and cleans your tank, meaning you have no need for replacement water.  

For this very reason our Auckland water tank cleaning service is very popular, given past challenges with getting fresh water.

Safe H2O clean water tanks by vacuuming out the sediment and then once this is removed, filter the remaining water through our purpose-built truck. 

This goes through 25 micron, 1 micron, and finally nanofiltration at 0.001 micron, filters that effectively remove any dangerous contaminants from the water.  

The purified water is returned to the tank meaning you do not need to purchase replacement water or draw additional water from a bore. 

We also add a small dose of food grade hydrogen peroxide as a belts and braces measure to ensure the water is safe and especially to flush the lines feeding off the water tank to ensure they are clean and safe. 

What are my legal obligations for water tank cleaning?

NZ Water regulation is in the process of changing with the introduction of the new water regulator Taumata Arowai.  Below is a quick summary of what this means for different situations.  Official information can be found at:  Guidance and resources | Taumata Arowai.

Private dwelling

In your own private dwelling you are responsible for your own water supply and there is no legal obligation to meet any minimum standard of care.  The recommendation to clean at least every two years is our expert guidance for you and your family.  We also recommend filtration.

Landlord – single dwelling
You have a legal responsibility to provide potable water to your tenants. Rainwater is considered potable. However, this does not take into account the surfaces the water contacts before being consumed.
There is case law where landlords have been prosecuted for not providing clean and safe water and were instructed to clean the tank and install filtration.
This is an extreme no-one would wish to reach and it seems a common-sense approach to follow the good practice of regularly cleaning your tanks and installing filtration at all times to ensure you are providing safe and clean water to your tenants.
Landlord – multiple dwellings e.g. larger farms with tenanted houses (including employees)
If your water source is supplying more than one dwelling then you are likely to be considered a small water supply under the auspices of the new water regulator, Taumata Arowai.
In short this means you need to develop and implement a water management plan complete with pre-tank preventative measures, and regular tank cleaning combined with a validated UV filtration system.
You need to implement the plan and maintain records to show your compliance. The level of regulation changes depending on the number of people using the supply and water source. We would be happy to provide more detailed guidance specific to your circumstances at any time.
Commercial uses
If you are using rainfed water for the preparation and serving of food and beverages then you do need to ensure your water is safe at all times.
This means meeting food hygiene requirements including developing and implementing a water management plan complete with pre-tank preventative measures, and regular tank cleaning combined with a validated UV filtration system.
You need to implement the plan and maintain records to show your compliance. We would be happy to provide more detailed guidance specific to your circumstances at any time.
Schools, Marae, Community Facilities
As the users of the water at such facilities can be a significant number of people, you are required by the water regulator, Taumata Arowai, to develop and implement a water management plan to follow an acceptable solution to ensure clean and safe water for all users.
This will include pre-tank preventative measures, and regular tank cleaning combined with a validated UV filtration system. You need to implement the plan and maintain records to show your compliance.
We would be happy to provide more detailed guidance specific to your circumstances at any time.
Should I use water filters?
Yes! Regular tank cleaning keeps the level of sediment in control but regardless of your water source and preventative measures, sediment build up is constant and ongoing.
Having some filtration at the pump means that you and your family are not being the filter in between tank cleans.
For rainwater supplies you cannot control what gets on your roof. This includes birds and bird droppings, which carry bacteria, including E-Coli.
While regular tank cleans minimise the risk of these bacteria multiplying nothing can remove the risk of them being present on an ongoing basis – other than filtration.
In conjunction with regular tank cleans this provides you and your family with the best protection going forward.
What filtration is right for me?
Typically you would install dual sediment filters – one higher micron filter e.g. 20 micron, being first in line to remove the larger sediment, followed by a 1 micron filter to remove finer sediment.
House filters tend not to go below 1 micron as going any finer starts to impact the water pressure in the house. In some cases a third filter is added – this is typically a carbon filter which helps remove odour and colour from water if that is required.
Bacteria tend to be 0.5 of a micron in size and therefore pass through the 1 micron filter. This is why people install a UV bulb in conjunction with the sediment filters. The UV light neutralises the bacteria and makes your water safe.
It is important to reiterate that the filters and regular tank cleans go hand in glove. One is not a substitute for the other. Without the regular tank clean your filters will be overworked and less effective e.g. the sediment in solution in the water will render the UV less effective as it blocks the UV light from reaching its target bacteria.
Please also note that what you legally need to do in terms of filtration can depend on your water source, who is using the water and what you are using it for. See above for our notes on legal obligations.
How much does it cost to clean my water tank?

The cost to clean your tank depends on a number of factors.  Read our blog post which details the factors involved in determining the cost to clean your water tank in NZ.  Further, we would be happy to discuss your circumstances at any time and provide an estimate.  Just call us on 0800 723342.

Water Saving Tips

Rainfed tank water is a limited supply and consequently is a precious resource to be conserved as much as possible. This is especially the case in the drier months of summer.

There are a number of key areas where the average household uses the most water – the kitchen, the bathroom and the laundry. In addition, attending to leaks and maximising your water catchment are great starting points.

There are a number of actions you can take to make sure you have ongoing access to clean and safe water on your property.

In addition to these detailed points, simply being aware of the need to conserve water will result in you using less water.

On your property
Maximise your rain catchment by cleaning all your guttering regularly and checking for leaks and blockages.
Check your home for leaks – dripping taps, showerheads and leaky toilets all contribute to water being wasted in the home. If your water pump is operating at times you are not using water e.g. during the night, then this is likely to mean you have a leak(s) that is/are activating the pump.
You can also consider installing water flow restrictor fittings on your shower and/or taps that minimise the amount of water wasted.
Water Leak Checklist:
  • Check all taps, inside and outside the home.
  • Look behind the dishwasher for any signs of water.
  • In dry weather, look for damp patches in the garden, lawn, or driveway.
  • Listen for the water pump working when you are not using water or running water inside your home when no taps, hoses, or showers are turned on.

If you discover the source of a leak, get in touch with a registered plumber if you cannot fix yourself.

In the bathroom
  • Turn off the water when brushing your teeth or shaving. You will use around one litre of water instead of five litres.
  • Limit your showers to four minutes or less.
  • Catch the water used when waiting for the shower to warm up in a bucket and use in your garden.
In the laundry
  • Wash full loads whenever possible. This will save water and energy.
  • Reduce the need to wash towels by hanging them in direct sunlight after use.
  • Change to water-efficient settings on your washing machine – an easy water-saving tip for the laundry is to use the economy settings on your washing machine. Reducing the wash to one rinse cycle rather than two will also save up to 100 litres of water per wash.
In the kitchen
  • When hand-washing dishes, fill the sink rather than rinsing and washing the dishes under a running tap.
  • Don’t leave your tap water running – the average tap uses 12 litres of water a minute.  Fill your sink or a bowl with the water you need and use this water e.g. to scrub vegetables.  This can be used to water plants afterwards.
  • Keep a jug of drinking water in the fridge – running your kitchen tap while waiting for the water to be cold wastes many litres of water. Instead, keep water in a covered jug in the fridge.
Around the property
  • Use a bucket of soapy water to clean windows or the car. Only use the hose for a quick spray to finish.
  • Sweep your paths and driveway rather than hosing.
Need a tank cleaning cost estimate?

If you do want a tank cleaning price estimate from Safe H2O, the easiest way is to tell us about your tank using our short form.

Or give us a call on 0800 723 342 – it usually takes a few minutes, and we can answer any questions you might have.

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