What’s in Your Water? Common Contaminants in NZ Drinking Water Tanks

Whether your water comes from rainfall, a bore or a nearby stream, one thing is for certain — your water tank isn’t just filling up with clean water.

It’s also collecting a range of unwanted contaminants that can affect the taste, smell and safety of your supply. 

At Safe H2O, we’re committed to helping Kiwis keep their water safe.

So, we’ve put together this guide to help you understand what might be lurking in your water tank — and what you can do about it. 

Sediment Build-up

Regardless of your water source, sediment is unavoidable. Rainwater tanks collect dust, dirt and debris from your roof and gutters. Stream or bore-fed systems often draw in fine silt, sand or clay — particularly after heavy rain or land movement. 

Why it matters: Over time, sediment settles at the bottom of your tank and builds up. This affects the clarity and taste of your water, can provide ideal conditions for bacterial growth, and can clog pipes, filters and pumps.  

Bird & Animal Droppings & Insect Debris

Birds, possums, rodents and insects are common culprits when it comes to tank contamination — especially in rural and coastal areas. Bird droppings on roofs can carry harmful bacteria like E. coli, Campylobacter and Salmonella, which easily wash into your tank during rain. 

Why it matters: These bacteria can cause serious illness if ingested and pose a risk to your family’s health. 

Tips:  

• Trim overhanging branches to remove easy access for animals to the roof 

• Fit gutter whiskers in gutters to minimise animals nesting in your roof and the larger debris washing into the tank 

• Fit mesh screens to your tank inlets to filter out larger debris  

• Inspect your roof and gutters regularly to keep clear and clean. 

• Inspect tank and pipe work/fittings for cracks 

• Install a UV filtration system to help remove sediment and bacteria before the water enters your home’s plumbing 

Tannins

If your water looks yellowish or has a funny taste, plant tannins may be to blame. These naturally occurring compounds come from leaves, bark and plant material that wash into your tank — especially after autumn leaves fall.

In NZ, tannins commonly come from trees like Pohutukawa, Manuka (tea tree), and Totara. 

Why it matters: Tannins don’t usually pose health risks, but they do affect taste and can stain bathroom, kitchen fittings, and washing. They can also reduce the effectiveness of UV filtration systems. 

Algae, Pollen & Organic Material

Algae thrive in warm, still water — but only when there’s access to sunlight. If any light is able to enter your tank, even through small cracks or an unsecured lid, it can create the perfect environment for algae and other organic growth.

Wind and rain can also carry in pollen, spores, and fine organic matter that settle in the water and contribute to contamination. 

Why it matters: Algae not only affect the taste and smell of your water, but certain types, can release harmful toxins that pose health risks to both humans and animals. 

Tip: Ensure your tank is well-sealed. Check regularly for cracks or gaps, and always keep the lid tightly secured to block sunlight and airborne contaminants, as well as insects. 

Pathogens: Giardia & Cryptosporidium

These microscopic parasites are common in New Zealand’s rivers and streams, particularly where livestock or wildlife are present. They’re generally chlorine-resistant and can survive in untreated water supplies for long periods. 

Why it matters: Both can cause gastrointestinal illnesses and are difficult to remove without specialist filtration. 

Tip: Get your tank cleaned regularly by the Safe H2O team – we filter your water to remove these pathogens. Along with regular cleaning, having a UV filtration system installed will ensure the water is safe year-round, by neutralising Giardia and Cryptosporidium before the water reaches your taps. 

Nitrates, Arsenic & Heavy Metals in Bore Water

Some regions in New Zealand — particularly Canterbury, Hawke’s Bay and Waikato — are known to have naturally occurring minerals or agricultural runoff affecting bore water. 

• Nitrates from fertilisers and animal waste are a growing concern in farming regions. 

• Iron & manganese: Cause staining and a metallic taste; often found in deeper groundwater sources and can impact UV filtration effectiveness. 

• Arsenic is found naturally in groundwater in some parts of the country e.g. geothermal areas. 

• Lead, zinc or copper can leach into water from old pipes, roofing or fittings. 

Why it matters: These contaminants may not change the smell or taste of your water — but long-term exposure can affect your health and/or can stop your UV filtration from working effectively. 

Roof Cleaning Chemicals: An Unexpected Culprit

Many homeowners use chemical roof treatments or moss killers themselves or engage a company to do this, without realising the impact on their water quality.

Even after rinsing and/or leaving the water supply disconnected until rain has washed the roof, residue can remain on the roof and make its way into your tank during the next rainfall. 

Why it matters: Chemical contamination can make your water unsafe to drink and may mean your entire tank needs to be drained – losing your precious water supply. 

Tip: If cleaning your roof, choose gentle, eco-friendly options such as baking soda or vinegar. Avoid harsh cleaners and always disconnect your downpipes during the process. 

The Good News? Safe H2O Can Help

At Safe H2O, we understand the unique challenges of maintaining clean tank water in New Zealand. That’s why we use a smarter, safer method that: 

• Removes sediment and organic matter without draining the tank 

• Filters water to remove microscopic contaminants that are bad for you 

• Treats water with food-grade hydrogen peroxide to ensure the water is safe 

• Preserves up to 90% of your existing water — saving you money and water 

Summing Up: What’s Really in Your Tank?

Contaminants in drinking water tanks are more common than many people realise. From animal droppings to nitrates, maintaining water quality takes more than just topping up your tank — it requires regular cleaning, filtration and attention to what’s getting in from your roof or water source. 

If you’re not sure what’s in your tank, you haven’t cleaned your tanks for some time or your water’s looking a bit off, we’re here to help.

Our advanced cleaning and filtration technology keeps your tank intact and your water safe — all without wasting the precious supply you’ve collected. 

Get in touch with Safe H2O today to book your next water tank clean — and enjoy the peace of mind of contaminant free water!