The short answer
They are two different things. Water purification tablets (usually chlorine or chlorine dioxide) go into water to kill germs, so you can drink water you're not sure about. Stable iodine tablets (potassium iodide) are a medicine you swallow to protect your thyroid after a nuclear reactor accident, and UKHSA says to take them only when officials tell you to. Iodine-based water tablets also exist, but the US CDC says people who are pregnant or have thyroid problems should avoid water treated with iodine. For most UK homes, stored bottled water comes first, then boiling, then chlorine-type tablets.
Two products with nearly the same name
People search for "iodine tablets for water" and "iodine tablets for radiation" as if they were one thing. They aren't.
| Water purification tablets | Stable iodine tablets (potassium iodide) | |
|---|---|---|
| What they're for | Killing germs in water you're not sure about | Protecting the thyroid from radioactive iodine |
| How you use them | Drop into water, wait, then drink the water | Swallow as a medicine, only when told to |
| Usual active ingredient | Chlorine (NaDCC) or chlorine dioxide; some use iodine | Potassium iodide |
| When you'd need them | Taps off, boil water notice, water you've collected | After a release from a nuclear reactor, if officials say so |
| Help against radiation? | No | Only for the thyroid, and only for radioactive iodine |
| Who says so | UK Chief Medical Officers, US CDC | UKHSA, US CDC |
Water purification tablets: what they do
They're a back-up for when you can't get safe tap or bottled water. The UK Chief Medical Officers' advice for a national power cut sets out the order:
- Drink bottled water and other safe drinks first. Be Ready suggests keeping 3 litres per person per day for 3 days.
- If you have to use other water, filter it through a coffee filter, pillowcase or sheet until it runs clear.
- Then boil it, or use water purification tablets, as long as they're in date.
- Last resort: about a quarter of a teaspoon of unscented household bleach per 10 litres, left for 15 minutes.
Boiling is the most reliable method. The Drinking Water Inspectorate says heating water is one of the best ways to kill bacteria, viruses and parasites, including Cryptosporidium.
Which tablets? The US CDC says iodine and chlorine tablets kill most germs but not Cryptosporidium, a parasite. Chlorine dioxide tablets do kill it, as long as you follow the instructions. Always follow the label for the dose and the waiting time, and check the expiry date.
What tablets can't do. The CDC says you can't make water with fuel, toxic chemicals or radioactive material safe by boiling or disinfecting it. Never drink floodwater.
Water purification tablets: best-sellers on Amazon UK, seen 3 November 2026
These water purification tablets were near the top of an Amazon UK search for "water purification tablets" on 3 November 2026, read through the Keepa price tracker. Keepa doesn't give star ratings, so we haven't shown them. Prices and ratings change all the time. We don't earn anything from Amazon or these products, and we haven't tested them: this is what shoppers were buying, not our recommendation.
| Tablets (as listed) | Pack | Price seen |
|---|---|---|
| Biocool Water Purification Tablets, 1 tablet treats 5 litres | 250 tablets | £23.99 |
| CleanPill Water Purification Tablets | 300 tablets | £24.00 |
| Ef-Chlor Water Purification Tablets, 167mg, 1 tablet treats 20 to 25 litres | 100 tablets | £15.00 |
| Emergency Water Purification Tablets, 1 tablet treats 1 litre (Hydrachem) | 100 tablets | £18.95 |
Listings don't always say which chemical is in the tablet. Before you buy, check the pack says chlorine (often NaDCC) or chlorine dioxide, how much water one tablet treats, and the expiry date. Of the tablet types, chlorine dioxide is the one the US CDC says kills Cryptosporidium.
Iodine water tablets: who should avoid them
Some water tablets use iodine instead of chlorine. They work on most germs, but the US CDC says:
- people who are pregnant, have thyroid problems, or are sensitive to iodine should avoid water treated with iodine
- nobody should drink iodine-treated water for more than a few weeks at a time
That's one reason chlorine or chlorine dioxide tablets are the simpler choice for a family kit.
Stable iodine tablets: a different job entirely
Stable iodine (potassium iodide) is a medicine. UKHSA says:
- It's for radiation emergencies at nuclear reactors that are running or shut down in the last 90 days.
- It works best if taken from 24 hours before to 2 hours after exposure to radioactive iodine.
- It must not be taken for the first time more than 24 hours after exposure.
- Take only the tablets provided for this purpose. Iodised salt is not a substitute.
The US CDC adds that it protects only the thyroid, and it will not help in a nuclear bomb emergency, where fallout harms you from outside the body. Getting inside and staying inside is the protection.
Stable iodine tablets are a pharmacy medicine in the UK. We don't link to or sell them. For who needs them and when, read should I buy iodine tablets?
What about water in a radiation emergency?
You don't need purification tablets for this. UKHSA says food and drink already indoors, including tap water, will be safe to consume, and mains water is unlikely to be affected straight away. You'll be told if that changes. That's another reason to keep some bottled water at home: it covers you whatever the emergency.
What to keep at home
- Bottled water first: 3 litres per person per day for 3 days (Be Ready). Our emergency supplies calculator works out your total.
- A pack of chlorine or chlorine dioxide tablets, in date, for collected water.
- A clean container with a lid to treat water in.
- A filter if you want one, used before tablets or boiling, not instead of them.
For the full method step by step, see how to make water safe to drink when the taps stop.
What to buy
About these links: plain links to ordinary retailer pages. We may earn from some links in future; we don't now. We haven’t tested these and we don’t rank them: they are examples that were in stock when we checked. Prices change. Check what you already own first. Full kit list
Bottled water
Look for: 3 litres per person per day for 3 days, for drinking. More for babies, pets and medical devices.
- Seven Oceans Emergency Drinking Water 0.5l (5-year shelf life) · EVAQ8 · £3.94 (price on 1 November 2026) Shop
Water purification tablets
Look for: In date. Follow the label: tablets come in different strengths. Filter cloudy water through a cloth first.
- Lifesystems Chlorine Dioxide Water Purification Tablets · Lifesystems (UK brand store) · £10.99 (price on 1 November 2026) Shop
- Lifesystems Chlorine Water Purification Tablets · Lifesystems (UK brand store) · £3.99 (price on 1 November 2026) Shop
- Aquatabs 397mg Water Purification Tablets (100 Pack) · Amazon UK · £53.55 (price on 1 November 2026) Shop
Water filter (optional)
Look for: Read what the maker says it removes. Keep tablets or a way to boil water as well.
- LifeStraw Personal Water Filter · Amazon UK · £25.80 (price on 1 November 2026) Shop
- LifeStraw Peak Series Solo Personal Water Filter · Amazon UK · £31.99 (price on 1 November 2026) Shop
- Lifesystems Water Filter Purifier Bottle · Lifesystems (UK brand store) · £49.99 (price on 1 November 2026) Shop
- Lifesystems Water Filter Purifier Soft Flask · Lifesystems (UK brand store) · £29.99 (price on 1 November 2026) Shop
Food-grade water containers with lids
Look for: Food-grade, with a lid, never one that held chemicals, fuel or paint. Date the water you store.
Frequently asked questions
Are iodine tablets the same as water purification tablets?
No. Stable iodine tablets (potassium iodide) are a medicine that protects the thyroid from radioactive iodine. Water purification tablets are dropped into water to kill germs. Some water tablets do use iodine, but they are a water treatment, not a radiation medicine, and you don't swallow them on their own.
Do iodine tablets purify water?
Iodine-based water tablets can. The US CDC says iodine and chlorine tablets kill most germs, but not Cryptosporidium, and that people who are pregnant, have thyroid problems or are sensitive to iodine should avoid water treated with iodine. Potassium iodide tablets for radiation are not a water treatment.
Which is better: purification tablets or a water filter?
They do different things. The US CDC says portable filters don't remove all germs, and most don't remove viruses, so it suggests filtering cloudy water first and then disinfecting it. Neither filters nor tablets make water with fuel, chemicals or radioactive material safe.
Do water purification tablets work against radiation?
No. The US CDC says you can't make water with fuel, toxic chemicals or radioactive material safe by boiling or disinfecting it. In a radiation emergency, UKHSA says tap water and drinks already inside your home are safe unless you're told otherwise.
What is the UK's official advice if the taps stop?
Use bottled water first. The UK Chief Medical Officers' script for a national power cut says to filter cloudy water through cloth until it runs clear, then boil it or use in-date purification tablets. Their last-resort method is about a quarter of a teaspoon of unscented household bleach per 10 litres, left for 15 minutes.
Should I buy iodine tablets just in case?
Most UK households don't need to. UKHSA says to take only the stable iodine tablets provided for this purpose, and only when officials say so. People living near nuclear sites are covered by their council's plan. We don't link to or sell iodine tablets.
Sources
We opened each page on the date shown. Official advice changes: if a source says something different now, follow the source.
- UKHSA (GOV.UK): What to do in a radiation emergency (updated 10 September 2024) (read 1 November 2026)
- UK Chief Medical Officers (GOV.UK, published 16 December 2025): Water and sanitation scripts for broadcast media, national power outage (read 1 November 2026)
- Drinking Water Inspectorate: Receiving a boil water notice (read 1 November 2026)
- GOV.UK Be Ready: be ready for emergencies (checklist) (read 1 November 2026)
- US CDC: How to make water safe in an emergency (19 September 2024) (read 1 November 2026)
- US CDC: Potassium iodide (KI) (read 1 November 2026)
Related guides
- Emergency water at home: how much to store and how
- No water supply: what to do, and what you're entitled to
- Boil water notice: what it means and what to do
- Radiation emergency in the UK: what official advice says (go in, stay in, tune in)
Free tools
- Emergency supplies calculator (how much water to keep)
- No water in my area: your water company's live page
We're an independent UK site, not the government. We check guides against official sources and link to them. In an emergency call 999.
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