What's in my water
Iron in water — why it stains, why it kills RO membranes, and how to remove it
Iron is a metal that dissolves into groundwater in its ferrous (Fe²⁺) form, invisible until it meets air and oxidises to ferric (Fe³⁺), which is the orange-brown particulate that stains everything it touches.
Limits and standards
BIS publishes two figures for many parameters: an acceptable limit, and a permissible limit that applies only where no alternate source of water exists. The second is a fallback for communities without a choice — not a target to design a purchase around.
| Standard | Limit | What it means |
|---|---|---|
| BIS IS 10500:2012 — acceptable limit | 0.3 mg/L | The 2012 revision removed the earlier permissible relaxation, so 0.3 mg/L is the single figure. |
| WHO | No health-based guideline value | WHO notes iron is not of health concern at concentrations found in drinking water, but that staining and taste become objectionable above roughly 0.3 mg/L. |
Where it comes from
Aquifer minerals
Iron-bearing rock and sediment dissolve under low-oxygen groundwater conditions. This is the dominant source and it is entirely natural.
Corroding iron pipework
Old galvanised iron distribution mains contribute, particularly after supply interruptions when pipes fill with air.
Borewell casing and pump components
Corroding steel casing adds iron directly at the point of extraction.
Iron bacteria
Naturally occurring bacteria that metabolise iron and produce a slimy reddish deposit in tanks and pipes, often mistaken for rust alone.
Why it matters
- It is primarily a nuisance and equipment problem rather than a health one — WHO does not set a health-based value.
- It stains sanitaryware, laundry and tiles orange-brown, and the stains are not removed by ordinary detergents.
- It gives water a metallic taste and can make tea and cooked food discolour.
- The expensive consequence is downstream: iron fouls RO membranes irreversibly and coats UV sleeves, quietly disabling equipment people paid for.
Note
Can you detect it yourself?
This is the section most purifier buying decisions skip. A handheld TDS meter is the instrument almost every Indian household is shown, and for most contaminants that matter it reads exactly the same whether the contaminant is present or not.
| Question | Answer |
|---|---|
| Can you sense it? | The most detectable contaminant on this list. Metallic taste, orange-brown staining, and the characteristic clear-to-orange change when water stands. Above about 1 mg/L it is unmistakable. |
| Does a TDS meter show it? | Dissolved ferrous iron does register slightly on a TDS meter, but it is not distinguishable from anything else. Once iron has oxidised to particulate, it stops contributing to conductivity altogether — so a heavily iron-fouled bucket of water can read low. |
| Field / home test | The bucket test is genuinely diagnostic and free: draw a glass, note it is clear, leave it 30 minutes. Orange sediment forming means dissolved ferrous iron. Colorimetric iron test kits give a usable number for under ₹500. |
| Laboratory test to ask for | Iron (total and dissolved) by AAS or ICP-OES — APHA 3111 B or 3120 B — ask for both total and dissolved, because the difference tells you how much has already oxidised (indicative ₹250–₹700) |
When to pay for a laboratory test
- Orange or brown staining on sanitaryware, or laundry coming out discoloured.
- You are about to install an RO system on a borewell. Test iron first — this is the single most useful pre-installation test, because getting it wrong destroys the membrane.
- Your RO membrane has failed early, more than once. Iron is the usual culprit and nobody checks for it.
- A slimy reddish deposit in the overhead tank, which suggests iron bacteria rather than iron alone.
What removes it
Effectiveness ratings below describe the technology working correctly, within its service life, on water or air that suits it. “Depends” means there is a condition in the caveat that decides the outcome — read it before buying.
- Oxidation + media filtrationEffective
>90% with correct contact time
Aeration or chemical oxidation converts ferrous to ferric, which is then filtered out on manganese greensand, birm or catalytic media. The standard, correct answer for borewell iron.
Caveat: Needs backwashing on a schedule. An iron filter that is never backwashed becomes an iron source.
- Sediment filtration (after oxidation)Partial
Once iron is oxidised to particulate, a 5–20 micron sediment cartridge captures much of it — which is why a pre-filter in an iron area clogs orange within weeks.
Caveat: Does nothing to dissolved ferrous iron, which passes straight through and oxidises afterwards.
- Reverse osmosis (RO)Depends
RO will reject dissolved iron, but running iron-bearing water into a membrane is how membranes die. Treat it as an outcome of last resort, not a strategy.
Caveat: Most RO manufacturers specify a maximum feed iron of around 0.1–0.3 mg/L. Exceeding it voids the effective life of the membrane and often the warranty.
- Ion exchange softenerDepends
A softener removes modest levels of dissolved ferrous iron along with hardness.
Caveat: Only for low, fully dissolved iron. Oxidised iron fouls the resin bed and is difficult to recover from.
- Chlorination + filtrationEffective
Effective and inexpensive, and it deals with iron bacteria at the same time.
Caveat: Requires a carbon stage afterwards to remove residual chlorine before any RO membrane.
What does not work
Each of these is commonly assumed — or actively marketed — to help with iron. None of them do.
UV
UV does nothing to iron — and iron does something to UV. Deposits on the quartz sleeve block transmission, so the lamp is on while the dose reaching the water collapses.
Activated carbon alone
Carbon fouls rapidly with iron and has little capacity for it. It is not an iron filter.
Boiling
Accelerates oxidation and leaves particulate iron in the vessel. It does not remove iron from the water you drink.
'Magnetic' or 'catalytic' descalers
Marketed for hardness and sometimes implied to help with iron. There is no mechanism by which they remove iron, and no credible evidence that they do.
Ferrous versus ferric, and why the bucket test works
Iron in groundwater is usually dissolved as ferrous iron, Fe²⁺. Dissolved means invisible: the water at the tap is genuinely clear, and people conclude it is fine.
Contact with air oxidises Fe²⁺ to Fe³⁺, which is not soluble. It comes out of solution as fine orange-brown particles — the rust colour in the bucket, the stain on the tiles, the sediment at the bottom of a standing glass.
This is why the bucket test is diagnostic. Water that is clear when drawn and orange after thirty minutes has dissolved iron, and any treatment that assumes it is a particulate problem will not work.
Important
The membrane failures nobody diagnoses
The single most common expensive mistake in Indian borewell water treatment is putting an RO system on iron-bearing water without pre-treatment.
The membrane fouls, output flow drops, TDS rejection falls, and the service technician replaces the membrane. Nothing upstream changes, so the new membrane fouls too. Two or three membranes later — several thousand rupees each — someone eventually tests the feed water.
Any RO installation on borewell water should begin with an iron result. A ₹250 test ahead of a ₹15,000 purchase is not a cost, and an installer who declines to do it is telling you something about how they work.
Frequently asked questions
Why does my water turn orange after some time in a bucket?
Does RO remove iron from water?
What is the best iron removal filter for borewell water?
Is iron in drinking water harmful?
How do I remove orange iron stains?
Sources
Every limit and standard quoted on this page comes from one of the documents below. Where a figure is not in one of these, we have not published it.
Bureau of Indian Standards · published 2012-05-01 · checked 2026-08-01
BIS states two figures for many parameters: an 'acceptable limit' and a 'permissible limit in the absence of an alternate source'. The second is a fallback for communities with no other supply, not a target.
Guidelines for Drinking-water Quality, 4th edition incorporating the 1st addendum
World Health Organization · published 2017-04-01 · checked 2026-08-01
Ground Water Quality in Shallow Aquifers — annual and state reports
Central Ground Water Board, Ministry of Jal Shakti, Government of India · checked 2026-08-01
District-level groundwater quality reporting. Coverage and sampling year vary by state — always check the report date for your district rather than assuming a national figure applies.
This page states what published standards say and what the physics of each technology allows. It does not state what is in your supply — no page can. Where the two questions meet is a test result, and every entry in this library says which test to ask for.