Reading Your Water Test Results — What Each Contaminant Means

If you’re on a bore or tank supply and you’ve just got a lab water test back, this guide is for you. A page of numbers, units and reference limits can be hard to read — but each line points to a specific problem and a specific fix. Below we walk through the contaminants that show up most often on New Zealand reports, what each means for your health and your plumbing, and the treatment it calls for. The golden rule: treat in the right order. And if you’d rather not decode it alone, send us the report — we read lab results free of charge.

E. coli and total coliforms — the line that matters most

Start here, because this is a safety line. Total coliforms are a broad group of bacteria that signal your water has been exposed to something it shouldn’t — soil, surface water, or a compromised tank. E. coli is more serious again: it’s a faecal indicator, meaning contamination from birds, possums, stock or septic seepage has reached your supply. Any E. coli detection means the water is not safe to drink untreated.

The proven fix is ultraviolet (UV) sterilisation, which kills bacteria and protozoa without chemicals. UV only works on clear water, so it always sits last in the chain, after fine sediment filtration to around 5 micron (1 micron ideal). A dose-rated class-A unit delivers 40 mJ/cm² and handles E. coli, giardia and cryptosporidium. Read more on our UV water treatment page.

Turbidity and sediment — the number that decides everything else

Turbidity measures cloudiness — fine particles of clay, silt, rust or organic matter suspended in the water, usually reported in NTU. High turbidity does two things: it looks and tastes bad, and it lets bacteria “hide” from UV light, so a high reading can render a UV lamp useless even when it’s working perfectly.

That’s why sediment cartridges come first in almost every system. A staged approach works best:
20 micron — catches the coarse grit and protects the pump.
5 micron — the minimum before UV.
1 micron — polishing for genuinely clear water. Get the sediment right and every stage after it performs the way the lab-report fix intends.

Iron, manganese, hardness and pH — the chemistry lines

These four are the everyday culprits on Waikato and wider NZ bore reports, and each has its own remedy:

Iron and manganese — the cause of rusty-orange or black-brown staining on fixtures and laundry, plus a metallic taste. Dissolved metals slip straight through a plain sediment filter, so they need an oxidising / iron-removal media stage that converts them to a solid the filter can trap. This goes before UV, because iron and manganese also foul quartz sleeves and shorten lamp life.
Hardness — high calcium and magnesium, reported as mg/L or grains. It’s safe to drink but leaves scale in kettles, cylinders and pipework and shortens appliance life. The fix is a water softener, which swaps the scale-forming minerals out.
pH — a low (acidic) pH below about 7 is common in soft bore and tank supplies and quietly corrodes copper pipe and hot-water cylinders, sometimes as blue-green staining. A neutralising filter lifts the pH into a safe range and protects your plumbing.

Nitrates and arsenic — the health lines that need specialist treatment

Nitrates turn up on rural reports where fertiliser and stock effluent leach into shallow groundwater. They’re of particular concern for bottle-fed infants, and standard sediment or carbon filters do not remove them. The reliable household fix is reverse osmosis (RO), usually fitted at the kitchen tap for drinking and cooking water.

Arsenic occurs naturally in the geology of some New Zealand areas and can exceed the drinking-water limit without changing taste or colour at all — the lab report is the only way you’ll know. It calls for a specialised adsorption media designed for arsenic, or reverse osmosis. Because the right media depends on the form and level of arsenic, this is one to talk through with us rather than guess. There’s a fuller rundown on our water contaminants reference.

Treat in the right order — and test again

The biggest mistake we see is treating out of sequence. Water should flow through your system in this order:
1. Sediment — clear the water first so everything downstream works.
2. Problem contaminants — iron/manganese media, softener, neutraliser, nitrate or arsenic treatment as your report requires.
3. UV last — sterilise clean, clear water for a reliable kill. Put UV first and iron, scale and turbidity will foul it within weeks. For a bore supply, our bore water treatment page shows how these stages fit together; for whole-of-house setups see water filtration systems. And retest annually — and always after a flood or heavy rain, when bacteria and turbidity spike.

Frequently asked questions

Can you read my water test report for me?

Yes — we read lab reports free of charge. Email your results to sales@pumpwarehouse.nz or call us, and we’ll tell you which lines matter, which are fine, and exactly what treatment (if any) you need. No obligation, and we won’t sell you a stage your report doesn’t call for.

How often should I test bore or tank water?

Test at least once a year for bacteria (E. coli and total coliforms), and get a fuller chemical test every couple of years or whenever the taste, colour or smell changes. Always retest after a flood, heavy rain or any work on the bore or tank, as contamination and turbidity commonly spike at those times.

My report is clear except for E. coli — do I really need the whole system?

Not necessarily. If bacteria are your only issue, you may need just sediment pre-filtration plus a UV unit — not softeners or specialist media. That’s exactly why reading the report first matters: it tells us the minimum system that makes your water safe, so you don’t over-spend.

Talk to the specialists

The Pump Warehouse has spent over 20 years helping New Zealand bore, tank and lifestyle-block owners get safe, clean water. Send us your lab report or call 0800 473 414 and we’ll turn those numbers into a plain-English plan. Visit us in Auckland (Rosedale) or Hamilton (Frankton, 34C Somerset Street — closed weekends), or email sales@pumpwarehouse.nz. You can also browse and buy through our online store, Pumps Online.