What causes brown water from hot water tap?
Quick answer: Brown water from your hot water tap is almost always caused by rust and dissolved iron. The most common sources are corroding iron or steel pipes, an ageing hot water system tank, or a disturbance to sediment that has built up inside your plumbing. The discolouration is usually a sign that iron particles have entered the water stream, and it tends to be more noticeable from the hot tap because heat accelerates corrosion.
Why does hot water turn brown?
Brown or reddish-brown water from the hot tap is a sign that iron or rust particles are present in your water supply. When iron corrodes inside pipes or a hot water storage tank, it forms iron oxide, which is the reddish-brown compound most people recognise as rust. That rust can flake or dissolve into the water flowing through your home.
The hot tap is often the first place you notice it because heat speeds up the corrosion process inside a storage hot water system. Cold water pipes can also corrode, but the problem tends to be more visible and more concentrated on the hot side, especially if your hot water unit is older or has not been serviced recently.
According to the Australian Drinking Water Guidelines (NHMRC), water supplied through rusting iron pipes can have iron concentrations of 5 mg/L or higher, well above the aesthetic guideline level.
What are the main causes?
Corroding iron or steel pipes
Older Australian homes, particularly those built before the 1970s, often have galvanised iron or mild steel pipes. Over time, the inside of these pipes corrodes and releases iron particles into the water. The Australian Drinking Water Guidelines note that iron concentrations in uncontaminated surface waters are usually less than 1 mg/L, but water supplied through rusting iron pipes can reach 5 mg/L or higher. That elevated concentration is what produces the visible brown colour.
An ageing hot water system tank
Most storage hot water systems use a steel tank with a sacrificial anode rod designed to slow internal corrosion. When the anode rod is depleted and not replaced, the tank itself begins to corrode from the inside. Rust flakes and iron-rich sediment accumulate at the bottom of the tank and are carried into your hot water supply. This is one of the most common reasons brown water appears specifically from the hot tap and not the cold.
Sediment disturbance
Iron and rust particles settle as sediment inside pipes and tanks over time. A sudden change in water pressure, nearby roadworks, a main break, or even a period of high demand can disturb that sediment and send it through your taps. This type of discolouration is often temporary and clears after running the tap for a few minutes, though it may recur if the underlying corrosion is not addressed.
Iron in the mains supply
In some areas, iron enters the water supply from the distribution network itself rather than from household plumbing. The Australian Drinking Water Guidelines state that in major Australian reticulated supplies, total iron concentrations range up to 4 mg/L, with typical concentrations around 0.1 mg/L. If your neighbours are also experiencing discolouration, the source is more likely to be the mains network than your own plumbing.
What do Australian guidelines say about iron in drinking water?
The Australian Drinking Water Guidelines (NHMRC) set an aesthetic guideline for iron based on taste and appearance rather than a health limit. The guidelines state that based on aesthetic considerations, including the precipitation of iron from solution and taste, the concentration of iron in drinking water should not exceed 0.3 mg/L.
The same guidelines note that iron has a taste threshold of about 0.3 mg/L in water and becomes objectionable above 3 mg/L. The guideline value of 0.3 mg/L is based on the taste threshold, which is similar to the concentration at which iron begins to precipitate out of solution and cause visible discolouration.
It is worth noting that the Australian guidelines treat iron primarily as an aesthetic concern. Visible brown water is unpleasant and can stain laundry, sinks and appliances, but the guidelines do not classify iron at typical household concentrations as a health hazard. If you are concerned about your specific water quality, contact your local water authority or a licensed plumber.
How to tell where the rust is coming from
A simple test can help you narrow down the source before calling a plumber.
- Run the cold tap first. If the cold water is also brown, the problem is likely in the mains supply or in shared cold-water pipes, not just your hot water system.
- Run the hot tap for several minutes. If the water clears after a few minutes, the rust is probably loose sediment that has been disturbed. If it stays brown, the corrosion is ongoing.
- Check with neighbours. If multiple households on your street have the same issue, contact your local water authority. They may be flushing mains or dealing with a pipe break.
- Inspect your hot water system. If your unit is more than ten years old and has not had its anode rod replaced, internal tank corrosion is a likely cause.
What to do about brown water from the hot tap
Flush the system
Run the affected tap at full flow for several minutes. This can clear loose sediment and temporarily restore clear water. If the discolouration returns quickly, the underlying source of corrosion needs attention.
Have your hot water system serviced
A licensed plumber or hot water technician can inspect the anode rod and flush sediment from the tank. Replacing a depleted anode rod is one of the most effective ways to slow internal tank corrosion and reduce rust in your hot water supply.
Consider pipe replacement
If your home has original galvanised iron pipes, repiping with copper or cross-linked polyethylene (PEX) is a longer-term solution. Copper pipes can also corrode over time, and the Australian Drinking Water Guidelines note that in premises with a history of copper corrosion, water that has been in stagnant contact for six hours or more with copper pipes and fittings should not be used in the preparation of food or drink. A plumber can advise on the best pipe material for your situation.
Filtration at the point of use
Where rust and iron are a concern at specific outlets, point-of-use filtration can help. The Evolved H2O Advanced Shower Filter helps reduce chlorine, heavy metals, rust, and other impurities in shower water. For bath water, the Evolved H2O Advanced Bath Filter removes rust. These are point-of-use options for shower and bath outlets; for concerns about drinking water quality, speak with your water authority or a licensed plumber about the appropriate solution for your home.
Key takeaways
- Brown water from the hot tap is most commonly caused by rust from corroding iron pipes, an ageing hot water tank, or disturbed sediment.
- The Australian Drinking Water Guidelines (NHMRC) set an aesthetic guideline of no more than 0.3 mg/L of iron, based on taste and the point at which iron precipitates visibly from solution.
- Iron in drinking water is treated as an aesthetic concern in Australian guidelines, not a health limit at typical household concentrations.
- Flushing the tap, servicing your hot water system, and replacing the anode rod are practical first steps.
- If neighbours are also affected, contact your local water authority, as the source may be the mains network.
Sources
- Iron | Australian Drinking Water Guidelines (NHMRC)
- Copper | Australian Drinking Water Guidelines (NHMRC)
Frequently Asked Questions
Is brown water from the hot tap dangerous to drink?
Australian drinking water guidelines treat iron primarily as an aesthetic concern rather than a health hazard at typical household concentrations. The guidelines set a guideline value of 0.3 mg/L based on taste and visible precipitation. If you are concerned about your specific water quality, contact your local water authority or a licensed health professional. This article does not constitute medical or health advice.
Why is the brown water only coming from the hot tap and not the cold?
Heat accelerates corrosion inside a storage hot water system. If the cold water runs clear, the source is most likely your hot water tank or the hot-water-side pipes rather than the mains supply or shared cold-water plumbing. An ageing tank with a depleted anode rod is a common cause.
Will the brown water clear on its own?
If the discolouration is caused by disturbed sediment, running the tap at full flow for several minutes often clears it temporarily. If the water stays brown or the problem recurs regularly, the underlying corrosion source needs to be addressed by a licensed plumber or hot water technician.
How much iron is normal in Australian tap water?
According to the Australian Drinking Water Guidelines (NHMRC), typical iron concentrations in major Australian reticulated supplies are around 0.1 mg/L, with concentrations ranging up to 4 mg/L. The aesthetic guideline is that iron should not exceed 0.3 mg/L.
Can I use brown water for showering or bathing?
Brown water with elevated iron can stain skin, hair, and surfaces. While Australian guidelines do not classify iron at typical concentrations as a health hazard, visibly discoloured water is generally best avoided until the source is identified and addressed. Contact your local water authority or a plumber for guidance specific to your situation.
What is an anode rod and why does it matter?
An anode rod is a sacrificial metal rod inside a storage hot water tank, designed to corrode in place of the tank itself. When the rod is fully depleted and not replaced, the steel tank begins to corrode internally, releasing rust and iron particles into your hot water supply. Regular servicing, including anode rod inspection, can significantly extend tank life and reduce rust in hot water.
