Wildfires
Wildfires can significantly affect the safety and sufficiency of a drinking water supply, not only while the fire is burning but possibly for weeks, months or even years afterwards.
This guidance is intended for small community supplies. However, much of the information is relevant to larger urban supplies and people who provide water for their own domestic use. Planning for wildfires and other natural hazard emergencies is essential.
Know the risks
During a wildfire
A burning wildfire can present immediate risks to your drinking water supply.
- Ash, soot and other debris could settle in surface water sources (streams, rivers and lakes) or on a roof used to collect rainwater for drinking. These substances might contain potentially harmful metals like manganese, iron and aluminium that could enter your water supply.
- Burning vegetation releases nutrients such as nitrogen and phosphorus, which could settle in surface water sources and increase the risk of algal blooms including cyanobacteria. Cyanobacteria can sometimes release toxins that are harmful to people and animals when consumed. Algal blooms are more likely if a wildfire increases the water temperature in rivers or streams.
- Ash and fire-retardant chemicals used for firefighting can change the pH (acidity/alkalinity) of your source water, which can cause metals like lead and arsenic and other harmful compounds to dissolve into the water.
- A wildfire might damage your drinking water infrastructure (e.g. pipes and storage tanks), cutting off your supply or causing breaks or leaks that allow microbiological (germs) and chemical contaminants into the water. Plastic pipes melted by the heat of a fire can sometimes release harmful chemicals into the water.
- A wildfire might cut the electricity supply, meaning your drinking water treatment system and pumps won’t be working.
- Water from your drinking water supply might be diverted for firefighting, reducing your ability to meet usual demand from your community.
After a wildfire
Depending on where your drinking water comes from, the location of the fire and the nature of the landscape around you, risks to your drinking water supply might continue well after the fire is out.
Vegetation slows the runoff of rainwater from land. If a wildfire removes vegetation from the catchment that feeds your drinking water source, runoff will increase and the quality of your water could be affected for weeks, months or even years after the fire.
- Increased soil erosion might lead to higher turbidity in surface water sources, which can prevent your treatment system from working properly.
- Increased soil erosion might increase the amount of decomposed plant or animal matter dissolved in surface water sources. This material is known as dissolved organic carbon (DOC) and can react with some disinfectants used for water treatment (e.g. chlorine) and create harmful disinfection byproducts.
- Some fire-retardant chemicals used for firefighting in the past contained polyfluorinated alkyl substances (PFAS), which are harmful to people. While PFAS are no longer used for firefighting, they can stay in the environment for many years (they’re known as ‘forever chemicals’), meaning they might still enter drinking water sources.
- Rain could continue washing ash, soot and fire-retardant chemicals into surface water sources long after the fire occurred. Runoff could come from the far reaches of the catchment, so even if the fire didn’t affect your supply immediately and directly it might have delayed and long-lasting impacts. Runoff can enter surface and groundwater sources.
- Heavy rain on bare ground could lead to flash flooding. Floods can damage supply infrastructure such as intakes and pipes, allowing microbiological (germs) and chemical contaminants to enter the water or possibly cutting off the supply altogether.
What to do during a wildfire
Your safety comes first
During a natural hazard emergency such as a wildfire, your safety, and the safety of the people in your community, comes first. Evacuate if Civil Defence, emergency services or your local authority advises you to, or if there’s an immediate risk to life or wellbeing.
Don’t attempt to check or repair your water supply until it’s safe to do so. If your supply uses rainwater collected from the roof and it’s safe to do so, disconnect the downpipes that feed your storage tank(s) so contaminated water doesn’t enter the tank(s).
If a wildfire is affecting your supply (e.g. ash or other debris are settling on or near your property, the power is off and/or the water looks, tastes or smells different), assume the water is contaminated and isn’t safe to use.
If possible, issue a Do Not Use Water notice and tell the people connected to your supply that they should use an alternative water source, such as bottled water or water from a registered water carrier, until you’ve checked that:
- your treatment system is working properly
- your source water is free from any contaminants or physical changes that your treatment system can’t cope with
- your distribution system is undamaged.
What to do after a wildfire
Assess your supply only when it is safe to do so
Once the fire is out and it’s safe to move around your property, check your source water and supply infrastructure for obvious signs of contamination or damage. Look for:
- ash, soot or other debris coating the water near your supply intake or the roof you use to collect rainwater
- broken or melted pipes
- damaged or destroyed storage tanks
- malfunctioning or destroyed pumps
- electricity cut to your treatment system
- cloudy or discoloured water, or water that smells or tastes different, coming out of taps.
Any of these signs indicate that your water might not be safe to use.
Here are some additional steps to take, depending on where your water comes from.
For supplies that use rainwater collected from the roof
Smoke, ash, soot and firefighting chemicals might have gathered on your roof during the fire (see Know the risks above).
Make sure your tank is disconnected, then clean away any debris or build-up on the roof. You might need to scrub the roof to remove soot and ash.
If you didn’t disconnect downpipes that feed water to the tank before rain, water in the tank might be contaminated. You can use water from the tank for cleaning the roof and other outdoor surfaces but don’t drink it.
After cleaning the roof, drain any remaining contaminated water from your tank and clean the tank before refilling it.
How to clean and disinfect your storage tank(s) and flush your pipes
Take extreme care when working at height or within the confines of the tank. Make sure you wear personal protective equipment (PPE) and someone is nearby to provide help if you need it.
If you have plain unscented bleach available, you might be able to disinfect your tanks using the following process. Don’t use bleaches that have detergents/surfactants (i.e. foam up when shaken), fragrances (e.g. lemon-scented) or are in gel form. Ideally use liquid bleach which contains 5 - 6% sodium hypochlorite.
- Calculate the volume of your tank
Circular tank: 3.142 x radius (in metres) x radius (in metres) x depth of water (in metres) x 1000 = number of litres. Radius = half the diameter (the widest part of the circle).
Square tank: Length (in metres) x width (in metres) x depth of water (in metres) x1000 = number of litres. - Add the required volume of unscented bleach shown in the table below and mix (you can use a broom handle or similar clean object to stir).
Tank volume (litres) Millilitres (ml) of bleach 500 35 1000 70 2000 140 5000 350 10,000 700
3. Turn on each tap and flush each toilet in the house or buildings until you smell chlorine and then close the tap. You are trying to get the chlorine solution to all parts of the plumbing. If there are any in-line filters, they should be removed and replaced with new filters after the disinfection is complete.
4. Allow the chlorine to sit in the pipes for at least two hours (preferably overnight).
5. Open all taps and flush out the chlorine solution for a couple of minutes to ensure it has passed through all pipes.
Test samples of untreated and treated water before giving the all-clear
Reconnect your tank to the roof and either have it filled from a safe source or wait for the next rain. If you wait for rain, it’s a good idea to then arrange for a sample of the untreated rainwater to be tested by an accredited laboratory for microbiological (germs) and chemical contaminants.
Check that there’s power to your treatment system and all electrical components (e.g. pumps, UV light disinfection unit) are working properly. If there are no problems and the laboratory has confirmed that your roof water is suitable for treatment, flush out all pipes by running all taps.
Arrange for a sample of your treated water to be tested by an accredited laboratory for microbiological (germs) contaminants. The laboratory can recommend which contaminants to test for and tell you how much it will cost.
Let the people connected to your supply know that the water is safe to use only after the laboratory has given the treated water the all-clear.
Act fast if laboratory tests indicate that your treated water is contaminated
If laboratory tests indicate that your treated water contains chemical contaminants or microbiological (germs), let the people connected to your supply know immediately.
- If laboratory tests show that your water contains chemicals that exceed their maximum acceptable valuable (MAV), issue a Do Not Use Water notice. Tell your community to continue using an alternative water source (e.g. bottled water, water from a registered water carrier) until your tank has been emptied, cleaned and refilled and pipes in your distribution network have been flushed.
- If the water contains microbiological contaminants (E. coli or total coliforms), issue a Boil Water notice. Boil all water used for drinking, washing dishes by hand, brushing teeth, preparing food, mixing baby formula, making ice and giving to pets – until further notice. Note that boiling water won’t get rid of chemical contaminants.
- If your supply is registered with us, notify us of the contamination as soon as possible. We can help you to re-establish a safe supply.
If testing indicates that your water may not be safe to drink or use over the long term, you may need to look at alternative supply options.
For supplies that use surface water sources (streams and rivers)
Ash, soot, debris and firefighting chemicals could be in the river or creek your drinking water comes from. These substances can carry metals like manganese, iron and aluminium, as well as nutrients like nitrate and phosphorus, into water sources (see Know the risks above).
If you store untreated water in a tank, there’s a chance it could be contaminated. Disconnect, then drain and clean any tanks that store untreated water.
How to clean and disinfect your storage tank(s) and flush your pipes
Take extreme care when working at height or within the confines of the tank. Make sure you wear personal protective equipment (PPE) and someone is nearby to provide help if you need it.
If you have plain unscented bleach available, you might be able to disinfect your tanks using the following process. Don’t use bleaches that have detergents/surfactants (i.e. foam up when shaken), fragrances (e.g. lemon-scented) or are in gel form. Ideally use liquid bleach which contains 5 - 6% sodium hypochlorite.
- Calculate the volume of your tank
Circular tank: 3.142 x radius (in metres) x radius (in metres) x depth of water (in metres) x 1000 = number of litres. Radius = half the diameter (the widest part of the circle).
Square tank: Length (in metres) x width (in metres) x depth of water (in metres) x1000 = number of litres. - Add the required volume of unscented bleach shown in the table below and mix (you can use a broom handle or similar clean object to stir).
Tank volume (litres) Millilitres (ml) of bleach 500 35 1000 70 2000 140 5000 350 10,000 700
3. Turn on each tap and flush each toilet in the house or buildings until you smell chlorine and then close the tap. You are trying to get the chlorine solution to all parts of the plumbing. If there are any in-line filters, they should be removed and replaced with new filters after the disinfection is complete.
4. Allow the chlorine to sit in the pipes for at least two hours (preferably overnight).
5. Open all taps and flush out the chlorine solution for a couple of minutes to ensure it has passed through all pipes.
Test samples of untreated and treated water before giving the all-clear
Before reconnecting the tanks, arrange for a sample of untreated source water to be tested by an accredited laboratory for microbiological (germs) and chemical contaminants and turbidity.
Check that there’s power to your treatment system and all components (e.g. pumps, UV disinfection unit) are working properly. If there are no problems and laboratory results have confirmed that your source water is suitable for treatment, reconnect the treatment system and then flush out all pipes by turning on all taps.
Arrange for samples of treated water to be tested by an accredited laboratory for microbiological (germs) and chemical contaminants. The laboratory can recommend which contaminants to test for and tell you how much it will cost.
Let the people connected to your supply know that the water is safe to use only after the laboratory has given the treated water the all-clear.
Act fast if laboratory tests indicate that your treated water is contaminated
If laboratory tests indicate that your treated water contains chemical contaminants or microbiological (germs), let the people connected to your supply know immediately.
- If laboratory tests show that your water contains chemicals that exceed their maximum acceptable valuable (MAV), issue a Do Not Use Water notice. Tell your community to continue using an alternative water source (e.g. bottled water, water from a registered water carrier) until your tank has been emptied, cleaned and refilled and pipes in your distribution network have been flushed.
- If the water contains microbiological contaminants (E. coli or total coliforms), issue a Boil Water notice. Boil all water used for drinking, washing dishes by hand, brushing teeth, preparing food, mixing baby formula, making ice and giving to pets – until further notice. Note that boiling water won’t get rid of chemical contaminants.
- If your supply is registered with us, notify us of the contamination as soon as possible. We can help you to re-establish a safe supply.
If testing indicates that your water may not be safe to drink or use over the long term, you may need to look at alternative supply options.
Planning for future wildfires
If your drinking water supply is in an area that’s prone to wildfires, preparation is key.
Your drinking water safety plan (required if your supply is registered with us and you are following the Drinking Water Quality Assurance Rules) or emergency risk management plan (required if you’re following an Acceptable Solution) should detail how you’ll respond if a wildfire occurs. It should cover the main risks to your supply and options for mitigating them, including:
- options for providing an alternative source of safe drinking water to your community (e.g. bottled water, trucking in water using a registered water carrier, establishing an emergency supply) if your supply is contaminated or cut off by a wildfire
- how you will communicate with the people who use your water if a wildfire affects, or threatens to affect, your supply
- key contacts, including Fire and Emergency New Zealand, Civil Defence, your local council, local registered water carriers, your nearest accredited laboratoryoutbound.
More information
Fire and Emergency New Zealand’s website includes tips for preparing for and responding to a wildfireoutbound. Helpful tips for drinking water suppliers include:
- clearing highly flammable vegetation from around buildings and other supply infrastructure
- not lighting fires when the risk is high
- planning escape routes for the community should a wildfire emergency occur.