Turning on the tap and seeing brown, orange, or cloudy water is understandably alarming. In most cases it's not an immediate health emergency, but it does need investigating. Here's a practical guide to understanding what's causing your discoloured water and what steps to take.
What Does the Colour Tell You?
The colour of your water is often the first clue to the cause:
- Brown or orange water – Usually indicates rust (iron oxide), either from your pipes, your hot water cylinder, or the mains supply.
- Yellow or tea-coloured water – Can suggest tannins from organic matter, particularly common in rural areas with tank water or bore water.
- White or milky water – Often caused by tiny air bubbles trapped under pressure. Fill a glass and let it sit — if it clears from the bottom up within a minute or two, air is the culprit and it's harmless.
- Black or grey water – May indicate manganese, mould, or degraded rubber fittings inside the system.
- Blue-green water – Points to copper corrosion, which can be a health concern and warrants prompt attention.
Common Causes in NZ Homes
Ageing or Corroding Pipes
Many older New Zealand homes — particularly those built before the 1970s — were plumbed with galvanised steel pipes. Over time, galvanised pipes corrode from the inside out, releasing rust particles into your water. If your home still has galvanised steel plumbing, discolouration is a strong sign that repiping should be on your radar.
Copper pipes are far more common in homes built from the 1970s onwards and are generally more durable, but they can still corrode if water chemistry is aggressive (low pH or high chlorine levels).
Hot Water Cylinder Corrosion
One of the most common causes of rusty water in NZ homes is a failing hot water cylinder. Most cylinders contain a sacrificial anode rod — typically magnesium or aluminium — designed to corrode in place of the cylinder lining. When this anode is depleted, the cylinder itself begins to rust. If only your hot water is discoloured, the cylinder is the most likely culprit. Cylinders typically last 10–20 years depending on water quality and maintenance.
Mains Supply Disturbance
If the discolouration affects both hot and cold water and came on suddenly, the issue may be with your local water supply. Watercare, Wellington Water, or your regional council supplier may have disturbed sediment in the mains during maintenance, a burst main repair, or a change in water flow direction. This usually clears within a few hours. Check with your local council or water supplier if you suspect this.
Tank or Bore Water
If you're on a rainwater tank or bore water system — common in rural New Zealand — discolouration can result from sediment, iron bacteria, tannins, or algae. BRANZ has useful guidance on rural water quality. Regular tank cleaning and appropriate filtration are important maintenance tasks for tank water users.
New Pipes or Recent Plumbing Work
After plumbing work or new pipe installation, it's normal to see brief discolouration as the system flushes out. Run the cold tap for a few minutes — if it clears quickly, there's generally nothing to worry about.
DIY Checks You Can Do
Before calling a plumber, run through these simple checks:
- Isolate hot vs cold – Run each separately. If only hot water is affected, focus on the cylinder.
- Check all taps – Is it one tap or the whole house? A single tap may have a corroded fitting or aerator.
- Let it run – Run the cold tap for 2–3 minutes. If the water clears, sediment was sitting in the pipes.
- Check with neighbours – If they have the same issue, it's likely a mains supply problem.
- Inspect your cylinder – Look for rust staining around the base or connections, which can indicate a leak or corrosion.
| Symptom | Likely Cause | Action |
|---|---|---|
| Only hot water affected | Failing cylinder or anode | Call a plumber |
| Both hot and cold, whole house | Mains disturbance or old pipes | Check with supplier; call plumber |
| One tap only | Corroded fitting or aerator | Clean or replace aerator; call plumber |
| Clears after running tap | Sediment in pipes | Monitor; repipe if recurring |
| Rural/tank water | Iron, tannins, or bacteria | Test water; install filtration |
| Blue-green tinge | Copper corrosion | Call plumber promptly |
Is Discoloured Water Safe?
Generally, brief discolouration from iron or sediment is not considered a serious health risk, but you should avoid drinking or cooking with it until it clears. Do not use discoloured water for infant formula, and avoid running it through appliances like washing machines (it can stain laundry). Blue-green water indicating copper corrosion should not be consumed and requires prompt professional attention. If in doubt, use bottled water until the issue is resolved.
For guidance on drinking water standards in New Zealand, MBIE Building Performance and your regional council are good starting points.
When to Call a Professional
Some plumbing work is restricted work under New Zealand law and must be carried out by a licensed plumber. This includes replacing or modifying your hot water cylinder, repiping your home, and any work on the toby (water meter) or connection to the mains. Attempting this work yourself is illegal and can void your home insurance.
You should call a licensed plumber if:
- Discolouration persists after running the taps for several minutes
- Only your hot water is affected (cylinder likely needs attention)
- You notice rust staining around your cylinder or pipes
- You have galvanised steel pipes and recurring rust issues
- Water has a blue-green tinge (copper corrosion)
- You're on tank water and unsure of water quality
The Plumbers, Gasfitters and Drainlayers Board (PGDB) maintains a register of licensed practitioners — always verify your plumber is licensed before work begins. You can also find qualified local plumbers on tradedirectory.co.nz.
Safety note: Never attempt to modify pressurised hot water systems yourself. Scalding water and pressure-related injuries are a real risk. Leave cylinder work to the professionals.