Kolkata · Water chemistry
Iron in Kolkata’s water — what it does, and how to get it out.
A practical guide to why so many Kolkata homes get iron-stained basins and yellow laundry, where the problem concentrates across the city, and the order treatment has to go in to actually work.
The problem you can see
Orange-stained basins, yellow laundry, metallic taste.
Iron in tap water is rarely the first thing a homeowner notices. The early signs are everyday: a faint orange tide-line around the basin drain, marble vanity tops that lose their polish, white shirts that come out of the wash with a yellow cast. Tea tastes metallic; coffee turns cloudy. None of it points at the supply until you connect the dots.
That is iron oxidising. Water that looks perfectly clear at the tap can leave a yellow-brown deposit once it meets air — on the side of the basin, inside the kettle, on the towel rail. The stain is rust. The fittings, the laundry, and the appliances are the visible record of what the water actually carries.
None of it is a cleaning problem. Stronger detergent, harsher descalers, and replacing the basin make no difference. The iron has to come out of the supply before it reaches the tap.
Why Kolkata homes get iron
Two supplies, two chemistries.
Central Kolkata — Park Street, Alipore, Ballygunge, Hindustan Park — runs largely on KMC treated municipal supply. Iron is usually below the BIS aesthetic limit of 0.3 mg/L at the tap; the lived problem is mild hardness scale and the occasional chlorine taste, not staining.
Cross the EM Bypass and the picture changes. Salt Lake, New Town, Rajarhat, and the Behala stretch sit on the city’s borewell belt — either fed wholly from groundwater or augmented when the KMC line is short. Borewell water in this belt commonly carries iron of 0.5–3.5 mg/L, well above the BIS limit, with hardness and TDS climbing alongside it.
The shift is not static. As Kolkata grows east, more apartment towers come online with private bores. The shallow water table is dropping, drawing iron-rich deeper aquifer water into more boreholes. Many homes that were on municipal-only supply five years ago now run on a mixed line — and that is when the first yellow stains appear.
Iron is a supply problem, not a fitting problem.
Water by locality
What the water reads, area by area in Kolkata.
Indicative ranges based on Uniwater survey data — confirmed on site.
| Locality | Supply | Iron | Hardness | TDS | Dominant issue | Typical system |
|---|---|---|---|---|---|---|
| Park Street | KMC treated | <0.3 ppm | 100–180 ppm | 180–320 ppm | Mild scale | BathSoft / Drinking |
| Alipore | KMC treated | <0.3 ppm | 120–200 ppm | 200–350 ppm | Light scale, taste | BathSoft / Drinking |
| Ballygunge | KMC treated | <0.3 ppm | 120–200 ppm | 200–350 ppm | Light scale | BathSoft / Drinking |
| Hindustan Park | KMC treated | <0.3 ppm | 120–200 ppm | 200–350 ppm | Light scale | BathSoft / Drinking |
| Tollygunge | KMC + borewell | 0.3–1 ppm | 150–280 ppm | 300–500 ppm | Scale, occasional staining | HomeSoft + BathSoft |
| Lake Town | Mixed | 0.5–2 ppm | 200–350 ppm | 350–650 ppm | Staining + scale | Iron filter + HomeSoft |
| Behala | Borewell/mixed | 0.5–2 ppm | 200–350 ppm | 350–650 ppm | Yellow staining, scale | Iron filter + HomeSoft |
| Salt Lake | Borewell/mixed | 0.5–3 ppm | 200–400 ppm | 400–800 ppm | Yellow stains, metallic taste, scale | Iron filter + HomeSoft |
| Rajarhat | Borewell | 0.8–3.5 ppm | 250–450 ppm | 500–900 ppm | Heavy staining + scale | Iron filter + HomeSoft |
| New Town | Borewell | 0.8–3.5 ppm | 250–450 ppm | 500–900 ppm | Heavy staining + scale | Iron filter + HomeSoft |
Park Street
Supply: KMC treated
- Iron
- <0.3 ppm
- Hardness
- 100–180 ppm
- TDS
- 180–320 ppm
Mild scale
BathSoft / Drinking
Alipore
Supply: KMC treated
- Iron
- <0.3 ppm
- Hardness
- 120–200 ppm
- TDS
- 200–350 ppm
Light scale, taste
BathSoft / Drinking
Ballygunge
Supply: KMC treated
- Iron
- <0.3 ppm
- Hardness
- 120–200 ppm
- TDS
- 200–350 ppm
Light scale
BathSoft / Drinking
Hindustan Park
Supply: KMC treated
- Iron
- <0.3 ppm
- Hardness
- 120–200 ppm
- TDS
- 200–350 ppm
Light scale
BathSoft / Drinking
Tollygunge
Supply: KMC + borewell
- Iron
- 0.3–1 ppm
- Hardness
- 150–280 ppm
- TDS
- 300–500 ppm
Scale, occasional staining
HomeSoft + BathSoft
Lake Town
Supply: Mixed
- Iron
- 0.5–2 ppm
- Hardness
- 200–350 ppm
- TDS
- 350–650 ppm
Staining + scale
Iron filter + HomeSoft
Behala
Supply: Borewell/mixed
- Iron
- 0.5–2 ppm
- Hardness
- 200–350 ppm
- TDS
- 350–650 ppm
Yellow staining, scale
Iron filter + HomeSoft
Salt Lake
Supply: Borewell/mixed
- Iron
- 0.5–3 ppm
- Hardness
- 200–400 ppm
- TDS
- 400–800 ppm
Yellow stains, metallic taste, scale
Iron filter + HomeSoft
Rajarhat
Supply: Borewell
- Iron
- 0.8–3.5 ppm
- Hardness
- 250–450 ppm
- TDS
- 500–900 ppm
Heavy staining + scale
Iron filter + HomeSoft
New Town
Supply: Borewell
- Iron
- 0.8–3.5 ppm
- Hardness
- 250–450 ppm
- TDS
- 500–900 ppm
Heavy staining + scale
Iron filter + HomeSoft
BIS acceptable limits (IS 10500): iron 0.3, hardness 200, TDS 500 mg/L.
A common confusion
“Does a water softener remove iron?”
No. A softener targets hardness — the calcium and magnesium that cause scale. Iron is a different problem with a different answer: a dedicated iron-removal filter that oxidises the iron and backwashes it out.
On most Kolkata borewell-fed homes the right answer is both, in the correct order: iron filter first, softener second. Skip the iron stage and dissolved iron coats the softener resin within months — the softener stops softening, and the homeowner ends up replacing resin instead of fixing the supply. The full answer is in the FAQ below.
How iron removal works
Oxidation. Media filtration. Backwash.
Dissolved iron is invisible. The filter has to convert it into a solid before it can catch it.
Oxidise.
Dissolved iron is exposed to an oxidising medium — catalytic manganese-oxide bed, or aeration upstream — and converts to insoluble iron particles.
Filter.
The newly-formed iron particles are caught on the media bed. Treated water leaves the vessel clear; iron stays in the bed until the next backwash cycle.
Backwash.
Periodically the flow is reversed at high velocity. The trapped iron is flushed to drain, the bed is re-graded, and the filter resets ready for the next service interval.
Why cheap iron filters fail
“Zero-maintenance” is marketing, not engineering.
Iron filters need backwashing on a schedule, and the media has a finite life. A unit sold as zero-maintenance is one whose owner stops being told what to do — not one that does not need doing. Skipped backwash compacts the bed. Compacted bed channels the flow; iron passes straight through.
The visible failure is the same as the original problem: yellow water, stained basins, metallic taste. The owner assumes the filter is broken and replaces the unit. The real fix was a backwash cycle and a media check — a five-minute job, every month, that none of the catalogue-grade units commit to.
What we specify in Kolkata
An iron filter, usually with a softener.
We survey first. The water test reads iron, hardness, TDS, and chlorine. The reading sizes the system. We do not quote without the survey.
Iron-removal filter
Stage one upstream of everything else.
Oxidising media in a vessel sized to your iron load. Monthly backwash and inspection rolled into the AMC.
See the iron filter →
Water softener (HomeSoft)
Sits downstream of the iron stage on borewell homes.
Ion-exchange resin in an FRP / SS316 vessel. Salt top-up and regeneration check on every service visit.
See the water softener →
Frequently asked
Iron in Kolkata water — common questions.
Does a water softener remove iron?
Why does my water turn yellow or orange after it stands?
How much does an iron filter cost in Kolkata?
Is borewell water in Salt Lake, New Town, or Rajarhat safe to use?
How often does an iron filter need servicing?
Related reading
Two journal pieces alongside this one.
Journal
Iron, then hardness — the right order.
Why iron pre-treatment has to come before softening on every borewell-fed train, and what happens when it doesn’t.
Read the journal →
Journal
The five-year cost of doing nothing.
Geysers replaced, basins re-glazed, laundry written off — the compounding cost of untreated borewell water on a luxury home.
Read the journal →
Your next step
Get the iron out at the source.
A free survey reads your water, sizes the system, and quotes a fixed price. Engineer at your door in 24 hours across Kolkata.