Is Your Water Tank Really Food Grade? How to Check Before You Buy
Almost every tank in an Indian hardware shop says “food grade” somewhere. The words cost nothing to print. To check whether a food grade water tank really is food grade, look for three things: an ISI mark with a CM/L licence number under IS 12701, a migration test report for the finished tank, and a virgin material declaration on the invoice or warranty card.
If you’re not sure yet why food grade matters, start with our guide on what a food grade water tank is and why you need one. This post picks up where that one stops. It’s about proof.
Why a “food grade” sticker isn’t proof
Picture two tanks side by side in a shop. Same colour, same “100% food grade” sticker, ₹2,000 apart in price. One has a licence number moulded into the body. The other has a sticker and nothing else.
That’s the problem in one picture. “Food grade” on a label is a claim. A licence number or a lab report is evidence. You want evidence, because you can’t see what’s inside a plastic wall, and you’ll be drinking from it for 10 years or more.
The 3 documents that prove a tank is food grade
| Document | What it proves | What it doesn’t prove |
|---|---|---|
| ISI licence under IS 12701 (CM/L number) | The tank meets the Indian standard for roto-moulded polyethylene water tanks: material, wall thickness, strength, stress cracking and safety for drinking water. BIS audits the factory. | Nothing about insulation, lids or antimicrobial claims |
| Migration test report | A lab has tested how much material moves from the plastic into water or a food simulant, and found it within limits. Look for standards like EU 10/2011 or IS 9845. | Strength or UV life of the tank |
| RoHS test | The material is free of restricted heavy metals such as lead and cadmium. | Migration of other substances |
A tank doesn’t need all three to be safe. But a tank with none of them is asking you to take its word for it.
How to read the ISI mark on a water tank
The ISI mark on a genuine tank has three parts. Check all three:
- The ISI logo itself.
- The standard number: for plastic water tanks this should read IS 12701. If it shows a different IS number, ask why.
- The licence number: written as CM/L- followed by a string of digits. P4’s Polyfoam ISI tank, for example, carries CM/L-5357874.
The mark is usually moulded into the tank body or printed on the label, often near the top. A logo with no CM/L number next to it is a warning sign.
Verify the CM/L number in 3 steps
This takes two minutes and you can do it standing in the shop.
- Install the BIS Care app (from the Bureau of Indian Standards) on your phone.
- Open “Verify Licence Details” and type in the CM/L number from the tank.
- Check the result: the licence should show as operative, the product should be water storage tanks to IS 12701, and the manufacturer’s name should match the brand on the tank.
If the licence is expired, belongs to a different product, or shows a manufacturer you’ve never heard of, don’t buy that tank.
How to read a migration test report
Many tanks, including premium foam tanks, aren’t sold under an ISI licence. For those, the migration test report is your main evidence. When the dealer hands you one, check these five lines:
- Who tested it. A named, accredited lab. Not the manufacturer’s own letterhead.
- Which standard. EU 10/2011 (the European rule for plastics touching food) or IS 9845 (the Indian method for overall migration) are both good signs.
- What was tested. The finished tank, or a sample from it. A certificate for the raw plastic granules only tells you the resin was food grade when it left the supplier.
- The result. It should say pass or “within limits”.
- The date. A report from the last few years is better than one from a decade ago.
That third point catches a lot of people. A resin certificate is useful, but it’s not the same as a test on the tank you’re buying.
Checks you can do yourself at the shop
Paperwork first, then use your eyes and nose:
- Look inside with your phone torch. The inner layer should be smooth and evenly coloured, with no black specks, streaks or bubbles. Specks can mean mixed or recycled material.
- Smell it. Put your head in the opening. A sharp chemical smell in a new tank is a bad sign.
- Match the label to the model. The certificate should name the same model and size you’re buying, not a different range from the same brand.
- Check the lid. A food grade body with a loose, thin lid still lets in dust and mosquitoes. Look for a lid that locks or screws down.
- Read the warranty card. It should mention virgin or food grade material by name. Keep it with the invoice.
Red flags
| What you see or hear | What it usually means |
|---|---|
| “Food grade” sticker, no ISI number, no test report | Unverified claim. Walk away for drinking water use. |
| ISI logo without a CM/L number | Not a valid ISI mark |
| CM/L number that doesn’t verify in the BIS Care app | Licence expired, wrong product, or fake |
| “The company has the certificate, we don’t” | Ask the brand’s customer care directly. Good brands will send it. |
| Only a resin supplier’s certificate | The raw plastic was food grade. The finished tank hasn’t been shown to be. |
| Price far below every branded tank of the same size | Something has been cut, often the material |
After you install: a 2-week check
Proof on paper is the start. Here’s how to check the tank once it’s on your roof:
- First fill: flush it. Fill the tank, let it stand a few hours, and drain it once before you use the water.
- Smell the water after a week of sun. Run the tap and smell a glass of water at 2 pm on a hot day. A plastic smell after the first flush is worth reporting to the brand.
- Look inside after two weeks. No film, no colour change on the inner wall.
- Clean every 6 months, and after the monsoon. Food grade material doesn’t stop sludge settling at the bottom.
Heat makes every one of these checks harder to pass, because warm water pulls more out of plastic than cold water does. That’s one reason foam insulation matters even for food safety. Read more on why the foam layer matters.
What P4 gives you as proof
Here’s what P4 publishes for its tanks, so you can check them the same way:
| P4 tank | Proof P4 publishes |
|---|---|
| Polyfoam ISI | ISI certified to IS 12701, licence CM/L-5357874; ROHS certified; BPA-free; 500 to 10,000 L |
| P4 International | Food grade inner layer; RoHS tested and migration tested to EU 10/2011; food grade test certificate available on request; 15-year warranty |
| P6 6 Layer PUF | Food grade inner layer; RoHS and EU 10/2011 migration tested; certificate available on request; 15-year warranty |
| P4 Food Grade | Food grade certified inner coating; 6 mm walls; 15-year warranty |
| Copper P4 International | RoHS and EU 10/2011 migration tested; P4 says copper levels meet drinking water standards (below 0.05 mg/L) |
Want ISI certification at the lowest price, for a shaded spot or a big building tank? Choose the Polyfoam ISI water tank. For an open rooftop where heat is the issue, choose a foam tank like the P4 Food Grade tank or the P4 International water tank, and ask the dealer or P4 customer care for the test certificate. Comparing brands? See Sintex vs Supreme vs Vectus vs P4.
FAQs
How do I check the ISI number of a water tank?
Find the CM/L number next to the ISI mark on the tank, then enter it in the BIS Care app under “Verify Licence Details”. It should show an operative licence for IS 12701 in the brand’s name.
Is a “food grade” sticker enough?
No. Anyone can print it. Look for an ISI licence number or a lab migration test report for the tank.
Does ISI mean the tank is food grade?
IS 12701 covers tanks for drinking water, and its requirements include safe material. So an ISI tank under IS 12701 is meant for potable water. Always check the CM/L number is real, though.
What is a migration test for a water tank?
A lab test that measures how much material moves from the plastic into water or a food simulant. A pass means the amount stays within safe limits.
Can I ask the dealer for the test certificate?
Yes, and you should. If the dealer doesn’t have it, ask the brand’s customer care. P4 says its food grade test certificate is available on request.