Enter your water volume, then a target dose — or let your iron and manganese test results set it
Volume & Dose
Tank Volume
Target Dose
Don't know your dose? Use your water testKMnO₄ needed = 0.94 × iron + 1.92 × manganese (mg/L)
Iron (Fe)
mg/L
Manganese (Mn)
mg/L
Enter your lab or test-kit results. The target dose above updates automatically. Hydrogen sulphide and organic matter use extra permanganate — confirm with a jar test (see below).
KMnO₄ Purity (optional)
Purity %
%
Use the purity on your product label. Technical-grade KMnO₄ is usually 97–99% pure; leave at 99% if unsure.
⚠ Please enter a valid tank volume and target concentration (both greater than zero).
WaterTankCalculator.com — KMnO₄ Dosage Results
Your Dosage Results
KMnO₄ to Add
—
grams of KMnO₄
Dose in mg/L
— mg/L
Tank Volume
— L
Volume in m³
— m³
Purity-Adjusted
— g
Dose Category
—
Contact Before Filtering
— min
Treatment Concentration Level
📖 How To Use
How to Use This Potassium Permanganate Dosage Calculator
Enter the volume of water to treat
Use litres, cubic metres, US gallons or UK gallons. For a partly full tank, enter the water actually in it. If you dose a flowing supply rather than a tank, enter the volume that passes in the time you're dosing for.
Set the dose — ideally from a water test
If you have a lab report or test-kit result, enter the iron and manganese levels and the calculator works out the dose from the chemistry. If not, enter a target dose in mg/L (the same as ppm). Most iron and manganese problems in household water need under 5 mg/L.
Enter the purity
Use the figure on your product label. Technical-grade KMnO₄ is usually 97–99% pure.
Confirm with a jar test, then treat
Before dosing a whole tank, test the dose on a small sample (see how to do a jar test). Organic matter and hydrogen sulphide use up extra permanganate that no calculator can predict.
Safety: Dissolve the crystals in a bucket of water first — never add dry crystals to a tank. Wear gloves and eye protection. KMnO₄ is a strong oxidiser: keep it away from glycerine, sugar, fuels and acids, which can react violently with it, and store it dry, sealed and out of reach of children.
📐 The Formula
Potassium Permanganate Dosage Formula
There are two steps: work out the dose the water needs, then convert that dose into grams for your volume.
Step 1 — Dose from a water test
KMnO₄ dose (mg/L) = 0.94 × Iron (mg/L) + 1.92 × Manganese (mg/L)
Example: well water with 2.0 mg/L iron and 0.5 mg/L manganese, 5,000 L tank, 99% KMnO₄
Dose = 0.94 × 2.0 + 1.92 × 0.5 = 1.88 + 0.96 = 2.84 mg/L
Grams = 5,000 × 2.84 ÷ 1,000 ÷ 0.99 = 14.3 g
The factors 0.94 and 1.92 come from the chemistry of the reactions: each milligram of dissolved iron uses about 0.94 mg of permanganate, and each milligram of manganese about 1.92 mg. They give the minimum dose. Anything else in the water that permanganate can react with — organic matter, hydrogen sulphide, some bacteria — adds to the demand, which is why a jar test matters.
What the water should end up below
Metal
Limit
Source
Why it matters
Iron
0.3 mg/L
US EPA secondary standard
Rusty colour, metallic taste, orange staining
Manganese
0.05 mg/L
US EPA secondary standard
Black staining, bitter taste
Manganese
0.08 mg/L
WHO health-based guideline
Long-term health effects at higher levels
Because permanganate itself contains manganese, overdosing can leave you with more manganese in the water than you started with. That's the main reason to dose to demand, not "a bit extra to be safe".
🧪 Jar Test
How to Check the Dose Before Treating the Whole Tank
Make a stock solutionDissolve 1 g of KMnO₄ in 1 litre of clean water. Each 1 mL of this solution added to 1 litre of sample equals a 1 mg/L dose.
Set up samplesFill several clear 1-litre jars with the water you want to treat.
Dose in stepsAdd different amounts to each jar — for example 1, 2, 3, 4 and 5 mL — stir, and wait 15–30 minutes.
Pick the lowest dose that worksChoose the lowest dose that leaves a very faint pink tint at the end of the wait. No pink means the permanganate has all been used up and some iron or manganese may remain; strong pink or purple means overdosed.
Reading the colour
Colour after contact time
What it means
What to do
Clear or yellow-brown, no pink
All permanganate used; may be under-dosed
Check iron and manganese after filtering; increase dose slightly if still high
Very faint pink
Slight excess — the usual target
Filter; the pink disappears in the filter or within a few hours
Strong pink or purple
Overdosed
Do not drink. Let it stand, dilute, or flush; reduce the dose next time
The brown-black particles that form are manganese dioxide — the iron and manganese you're removing, now in solid form. They must be filtered or allowed to settle and drained off. Permanganate treatment without filtration just turns dissolved metals into floating particles.
💡 Use Cases
When Potassium Permanganate Is — and Isn't — the Right Choice
Iron and manganese in well or bore water
This is what KMnO₄ does best. It turns dissolved iron and manganese into particles that a sand or manganese greensand filter can catch. Signs you need it: orange or black staining on fixtures, a metallic taste, or water that comes out clear and turns brown after standing. Get the water tested first so you can dose from the actual iron and manganese levels.
Rotten-egg smell (hydrogen sulphide)
Permanganate also oxidises hydrogen sulphide, but the amount it needs varies a lot with the water, so a jar test is essential. If the smell comes only from the hot water, the cause is often the water heater rather than the supply.
Musty tastes and odours
KMnO₄ can reduce some taste and odour compounds. In a storage tank, though, these usually come from sediment, biofilm or light getting in. Cleaning the tank and sealing the lid is the lasting fix.
Not for killing germs
Adding permanganate to a well or tank until the water turns pink is a common traditional practice, but it is not a reliable way to disinfect drinking water. To make water safe from bacteria and viruses, use chlorine — see our chlorine dosage calculator or bleach to water ratio calculator. Where both are used, permanganate goes first to remove the metals, then chlorine to disinfect.
Drinking water: never drink water that is still pink or purple, or that contains brown particles. Filter it, and check that iron and manganese are below the limits above before relying on it.
❓ FAQ
Frequently Asked Questions
How much potassium permanganate do I need for my water tank?
It depends on how much iron and manganese is in the water. The dose in mg/L is 0.94 × iron + 1.92 × manganese. Multiply that by your volume in litres and divide by 1,000 to get grams. For example, water with 2 mg/L iron and 0.5 mg/L manganese needs about 2.84 mg/L, which is roughly 14 grams for a 5,000-litre tank. Confirm with a jar test, because organic matter and hydrogen sulphide add to the demand.
Can I drink water treated with potassium permanganate?
Only after it has been filtered and is completely clear, with no pink colour and no brown particles. Permanganate adds manganese to the water, and the US EPA's secondary standard for manganese is 0.05 mg/L, while WHO's health-based guideline is 0.08 mg/L. Overdosing can push manganese above these levels, so dose to demand and test the treated water if you rely on it for drinking.
Does potassium permanganate disinfect water?
Not reliably. It's a strong oxidiser that's excellent for removing iron, manganese and some odours, but it isn't a dependable way to kill bacteria and viruses in drinking water. Use chlorine for disinfection — see our Chlorine Dosage Calculator. When both are needed, permanganate goes first and chlorine second.
What does it mean if my water stays pink or purple?
There's more permanganate than the water needed. A very faint pink at the end of the contact time is normal and is usually the target, because it shows there was enough to react with all the iron and manganese. Strong pink or purple means you overdosed — don't drink it. Let it stand, dilute it with fresh water, or flush the tank, and use a lower dose next time.
What are the brown or black particles after treatment?
They're the iron and manganese you're trying to remove, now oxidised into solid particles (mostly iron oxides and manganese dioxide). That means the treatment worked. They have to be filtered out or allowed to settle and drained off. They also stain tank walls brown-black over time; a dilute citric acid solution removes the staining.
How long should potassium permanganate stay in the water?
The reaction with iron and manganese is usually quick — the jar test uses 15–30 minutes, and many treatment systems give 10–30 minutes of contact before the filter. Hydrogen sulphide and organic matter can take longer. The jar test is the best guide for your water: use the contact time at which the lowest dose leaves only a faint pink.
How do I dissolve potassium permanganate before adding it to a tank?
Stir the crystals into a bucket of clean water until fully dissolved — it turns deep purple. Pour it in slowly while the tank is filling or while mixing, so it spreads evenly. Never add dry crystals straight to a tank: they sink, dissolve unevenly and stain whatever they land on. Wear gloves and eye protection, and rinse any spills immediately.
✅ Sources & Review
Sources and review
The limits and chemistry on this page come from these references:
Permanganate demand of 0.94 mg/mg for iron and 1.92 mg/mg for manganese, from the reaction stoichiometry used in standard water treatment references.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects, including treatment of well water containing iron and manganese. John writes and reviews every calculator on this site.
