Earthquakes
Earthquakes can severely affect a drinking water supply. In our quake-prone country, it’s essential that drinking water suppliers prepare. Learn about the risks and steps you can take to be ready.
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 earthquakes and other natural hazards is essential.
Know the risks
A major earthquake is likely to have significant direct and indirect impacts on your drinking water supply.
- Ground shaking and associated landslides and liquefaction could cause significant damage to parts of your supply, including:
- water pipes (particularly underground pipes)
- storage tanks
- bore shafts and headworks
- pumps
- electrical works
- water treatment equipment
- buildings containing water treatment equipment.
- Some damage could allow harmful microbiological (germs) and chemical contaminants to enter the water, result in inadequate treatment, or cut off the supply altogether.
- Ruptured sewage systems (including septic tanks) or chemical/fuel storage facilities near damaged drinking water infrastructure might increase the risk of contaminants entering the water.
- Power might be cut for several days, or possibly weeks in remote areas, meaning water treatment systems and pumps won’t be working.
- Ground shaking, landslides and liquefaction might lead to increased turbidity in surface and groundwater sources (cloudiness or haziness caused by dirt and other suspended particles), which might prevent treatment systems and pumps from working properly. Turbidity could remain high for some time after the earthquake, as loosened soil and debris are washed into waterways from the far reaches of the catchment and aftershocks cause further landslides and liquefaction.
- A major earthquake could physically change surface and groundwater sources (e.g. by blocking or re-routing streams or causing fluctuations in aquifer levels), meaning you might not have enough water for your supply.
- Ground shaking might disrupt the layers of soil and rock that act as natural filters for groundwater, allowing contaminants such as agricultural runoff, sewage and naturally occurring minerals and compounds to seep in.
- Communication networks (e.g. mobile networks) might be out of action for some time. It could be difficult to contact people who can provide emergency support (e.g. emergency services, Civil Defence, your local council, registered water carriers, the nearest accredited laboratory).
- Damage to roads and disruptions to supply chains could prevent or hinder access to alternative drinking water sources (e.g. bottled water or water from a registered water carrier).
What to do after an earthquake
As a precaution, assume your supply is contaminated
After a major earthquake, assume that the water from your supply is contaminated and isn’t safe to use.
Tell the people connected to your supply that they should use an alternative source (e.g. bottled water, water from a registered water carrier) until further notice. If it’s safe to do so, place a Do Not Use Water notice on taps connected to your supply until you’ve completed the checks and tests below and confirmed that the water is safe.
Assess your supply only when it’s safe to do so
Once it’s safe to move around your property, check your source water and supply infrastructure for obvious signs of contamination or damage. Look for:
- cloudy or discoloured water, or water that smells or tastes different, coming out of taps
- impacts on your source water and source water infrastructure, such as changes in river flows and turbidity and damage to water intakes, bore shafts and heads, or roofs and tanks used to collect rainwater
- broken or leaking pipes
- visible contaminants (e.g. sewage, agricultural runoff, fuel/chemicals) in the area of your water supply infrastructure
- malfunctioning or damaged pumps
- electricity cut to your treatment system
- damage to components of your treatment system (e.g. cracks or leaks in cartridge filters or UV light disinfection units and the pipes connected to them).
Any of these signs indicate that your water might not be safe to use.
Even if your supply appears intact and your treatment system seems to be working properly, assume the water is contaminated. Remember, not all contaminants can be seen, smelled or tasted. It’s also possible that an earthquake will introduce contaminants that your treatment system isn’t designed to manage. These could pass through undetected and untreated.
Provide an alternative water source
Alternative water sources include bottled water or water from a registered water carrier service (‘water tanker’).
The availability of alternative sources will depend on the severity of the earthquake’s impacts in your area. For example, it might not be safe to deliver bottled water to your community or possible for a water carrier to access your area quickly. That’s why planning and preparation are critical (see below).
If you are providing an alternative water source to your community, notify us as soon as you can. We can provide support and further advice on how to protect the health of you and your community.
Establish an emergency supply if a safe alternative supply isn't available
If your existing supply is unusable or has failed and an alternative safe water source isn’t available, there is provision under the Water Services Act 2021 for you to set up an unplanned emergency supply.
The Act requires you to provide water that’s safe to drink as far as reasonably practicable. However, it may be that you need to establish a supply quickly using whatever water source is available. If so, tell the people connected to your supply to use one of the steps under How to disinfect water if no alternative source is available below.
If you need to establish an unplanned emergency supply for your community, notify us as soon as possible. We can provide support and further advice on how to protect the health of you and your community.
Find out more about establishing an unplanned emergency supply
How to disinfect water if no alternative source is available
If it isn’t possible for you to provide an alternative source of safe drinking water to your community after an earthquake, there are steps you and your community can take to disinfect water. These include boiling the water or disinfecting it with bleach.
These steps will protect against microbiological contamination (germs) but not chemical contamination. Many chemical contaminants shouldn’t present a health risk in the short term. However, if there’s obvious evidence of chemical contamination (e.g. a smell of petrochemicals, evidence of damage to a drum of pesticide stored close to the source), then the water should be used with absolute caution.
Further checks before re-establishing your supply
If it appears that your source water is unaffected, your treatment system is operating properly and your distribution network is undamaged, there are a number of things you should still do before re-establishing the supply.
Wait for any turbidity in your source water to reduce
High turbidity can stop treatment processes such as chlorination and UV light disinfection from working properly. An earthquake can raise the turbidity of your source water, so it’s important to wait until turbidity returns to normal before re-establishing your supply.
You can test the turbidity of your source water using a hand-held device called a turbidimeter or send samples to an accredited laboratory for testing.
Check electrical systems fully
Check electrical systems (e.g. UV disinfection unit, pumps) carefully. If there’s any risk, wait until a qualified electrician can perform a full safety test.
Check the UV transmittance of your UV disinfection equipment to ensure it delivers the correct dose. Contact a specialist technician for assistance if required and continue to use an alternative water source until you’re sure the system is working properly.
Clean and disinfect your storage tank(s) and flush your pipes
Divert any water collected in storage tanks following the earthquake to waste, then clean and disinfect the tanks – taking extreme care when working at height or within the confines of the tank. Make sure you wear personal protective equipment (PPE) and there’s someone nearby at all times in case you need help.
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 litresRadius = 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) Millitres (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, remove them and replace them 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.
Arrange for an accredited laboratory to test your water
If it’s possible to do so, arrange for samples of your source water and treated water to be tested by an accredited laboratory for microbiological contaminants (E. coli and total coliforms), chemical contaminants (iron, manganese, nitrate, boron and ‘hardness’) and physical properties (turbidity, UV transmittance and pH).
Talk to your accredited laboratory for any additional tests that might be needed. The laboratory can explain what testing is recommended and how much it costs.
If laboratory tests show that your water contains chemicals that exceed their maximum acceptable valuable (MAV), keep the Do Not Use Water notice in place. Tell your community to continue using an alternative water source (e.g. bottled water, water from a registered water carrier).
If the water contains only microbiological contaminants (E. coli or total coliforms), issue a Boil Water notice instead. 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.
Don’t lift the notice until laboratory tests have given the all-clear.
Prepare for earthquakes
New Zealand lies on the boundary of the Pacific and Australian tectonic plates, so earthquakes happen here every day. Most are too weak, too deep or too far offshore to be noticed. However, a strong, damaging earthquake can happen at any time and can be followed by aftershocks that continue for a long time.
Seismologists know the locations of many large faultlines in New Zealand. However, there are many other faults buried underground that they don’t know about. Everywhere in New Zealand is at risk of earthquake hazards.
Drinking water suppliers in all parts of the country should prepare for earthquakes
Your drinking water safety plan (required if you’re following the Drinking Water Quality Assurance Rules) or emergency risk management plan (required if you’re following an Acceptable Solution) should detail ways you can provide safe drinking water when your supply is disrupted or you’re unsure whether the water is safe to use. Your plan should list sources of bottled water and registered water carriers who serve your area.
Keep a printout of your plan in a prominent place so you can access it quickly in an emergency.
There are other simple things you can do to prepare.
- Keep critical spare parts for your treatment system (e.g. filter cartridges, UV lamps, UV quartz sleeves), any tools needed for repairs and replacements, and manufacturers’ manuals handy and easily accessible.
- Look for ways that you can reduce the risk of damage to supply infrastructure and your treatment system during an earthquake. For example:
- if possible, locate treatment plants, pumping stations, storage tanks etc on ground that isn’t subject to liquefaction or in the likely path of landslides
- choose earthquake-resistant materials for key supply infrastructure (e.g. plastic above-ground tanks, seismic-resistant pipes, seismic-resistant buildings to house treatment equipment)
- keep large unsecured items well clear of treatment system components to reduce the likelihood that the system will be damaged by falling objects during an earthquake
- install seismic restraints on treatment equipment, particularly large, freestanding items (e.g. softeners, backwashable filters).
- Consider multiple water sources (e.g. surface water and groundwater or groundwater and roof water) so a backup is available if an earthquake damages or cuts off your primary source.
- Obtain a generator you can use to keep your treatment system working in case of a prolonged power cut.
- Know how you can contact the people connected to your supply so you can share important information with them about the status of the water supply. Remember that power, internet and mobile phone services could be cut for some time after a major earthquake.
- Print out a supply of consumer advisory notices (e.g. Boil Water notices, Do Not Drink notices) and keep them handy so you can put them up quickly after a major earthquake.
Find printable notice templates and information about how to use them.
Encourage the people connected to your supply to prepare
Tell members of your community that they should hold enough bottled water to meet demand for at least three days (allow for three litres per person per day – enough for drinking and basic hygiene). It could take at least this long for local authorities to establish drinking water stations after a major earthquake.
In case there’s a long delay before the power is back on and/or safe drinking water is available, it’s a good idea for you and your community to have a way of boiling water (e.g. gas-powered camping stove) or disinfecting water (a bottle of plain unscented bleach) on hand. See How to disinfect water if no alternative source is available above.
More information
The New Zealand Government’s Get Ready website has information you can share with your community about storing water for emergency useoutbound and other ways to prepare for a natural hazard emergency.
Water New Zealand, Opus and GNS Science (now Earth Sciences New Zealand) have produced seismic assessment and design guidelines for underground utilitiesoutbound.
Your local Civil Defence Emergency Management group and council should also have information specific to your area that you can share with your community.