You can do a lot of your own tank maintenance, such as clearing gutters, checking screens and treating the water. Getting inside a tank to clean it is a different matter. WorkSafe lists storage tanks as an example of a confined space, where low oxygen or harmful air can cause unconsciousness and death. Health New Zealand’s advice is that tank cleaning should ideally be carried out by tank cleaning contractors.
Here is what is reasonable to do yourself, what to leave alone, and how to treat your tank water safely.
What you can safely do yourself
Most of the work that keeps a tank clean happens outside it.
Keep the roof and gutters clear
What lands on the roof ends up in the tank. Clearing gutters, leaf guards and first-flush diverters is the single most useful job you can do. Level, the BRANZ sustainable building site, suggests doing this every three to six months.
Check the lid, screens and inlets
Look for gaps where birds, rodents or insects could get in, and make sure the lid sits properly. Kaipara District Council advises keeping the tank covered to prevent contamination from animals and birds.
Remove sediment from outside the tank
Health New Zealand describes a few ways to remove sediment without getting in, including an automatic tank vacuum system, an inverted funnel on a hose moved across the tank floor, or a swimming pool vacuum cleaner. These are slow and fiddly, but they keep you out of the tank.
Change your filters
The Waterboy recommends changing household filters every six months, and stocks most common types.
Why getting inside a tank is risky
A water tank does not look dangerous. It is the air inside, and the difficulty of getting out, that cause problems.
WorkSafe defines a confined space as an enclosed or partially enclosed space not designed for people to occupy, which may have unsafe levels of oxygen, harmful airborne contaminants or flammable substances. It names storage tanks as an example. The hazards WorkSafe lists include oxygen-deficient atmospheres, “which can cause unconsciousness, brain damage and death”, and toxic atmospheres from gases, vapours or fumes.
WorkSafe’s core principle is blunt: “Don’t go in if you don’t have to.” Check first whether the job can be done with equipment from outside the space.
If you do decide to go in, the minimum precautions from official guidance are:
- Health New Zealand: “ensure there is adequate ventilation and another person present.”
- Level (BRANZ): tell someone what you are doing and agree to check back with them when the job is done.
Other risks are practical. Tank floors are slippery, access hatches are small, and climbing out with a bucket of sludge is harder than it sounds. Disturbing the sludge can also stir up whatever has been sitting on the bottom.
How to treat your tank water
Treating the water is different from cleaning the tank. It deals with bacteria but does not remove sediment. The Waterboy’s recommended treatments for home use are Pour N Go or plain original bleach.
Treating with Pour N Go
Pour N Go is sold at retailers including Mitre 10 and Bunnings. Its distributor says it is approved in New Zealand as a water treatment chemical (NZFSA C61), is tasteless and odourless, and breaks down into oxygen and water as it reacts.
Dose rates are printed on the label, with a chart for different tank sizes. The manufacturer applies it through the access hatch and mixes it by spraying over the surface, stirring with a paddle, or running a hose back into the tank. Roofs in dusty areas or with lots of birds need more frequent treatment.
Treating with bleach
Guidance supplied by the Ministry of Health, published by Wairoa District Council, is that after cleaning you can disinfect a tank with about 167 ml (about two thirds of a cup) of household bleach per 1,000 litres of water. The bleach water is run through all your household pipes and taps until it is gone, and the clean tank is then refilled.
Health New Zealand’s advice is to use plain, unperfumed household bleach. It also notes that some parasites are resistant to chlorine.
Always read the label and specifications of any product you use to treat drinking water.
Keep it going
The Waterboy’s experience is that treating a tank needs to be an ongoing process to work. Gutter-fed tanks will always pick up some bacteria from the roof. That matters most for anyone with a weakened immune system, and Health New Zealand warns contaminated water can be particularly dangerous for infants and the elderly too.
Boiling as a backup
Health New Zealand says boiling water for one minute is the simplest and most effective way to reliably kill Cryptosporidium and other germs. It is a good stopgap, but it does not fix the underlying problem in the tank.
Longer-term protection
Taumata Arowai, the water services regulator, recommends households on their own supply learn about end-point treatment, using cartridge filters, UV light and backflow prevention, and consider regular testing through an accredited laboratory.
When to call a professional
Call a tank cleaning contractor if:
- the sludge layer is thick, or is being drawn into your outlet
- the water smells, tastes odd or is discoloured
- an animal has died in the tank
- someone in the house has been unwell and the tank is a suspect
- you would have to enter the tank to do the job
The Waterboy offers two services. A tank vacuum ($280 including GST) removes sediment from the lid without anyone entering the tank, taking out up to about 1,500 litres of water. A full drain and scrub ($450 including GST) is for contaminated water or very heavy sediment, and is done by our team, not by you. Both prices are per tank. See the tank cleaning service page for details.
For how often to inspect and clean, read our guide on how often you should clean your water tank.
Need water or a tank clean in Mangawhai?
The Waterboy cleans tanks and delivers Taumata Arowai certified, UV treated bore water across Mangawhai. Call 0800 426 269 to book a tank clean, or book a water delivery online to refill afterwards.
- tank cleaning
- water tank
- DIY
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- water treatment