How to Purify Water in an Emergency: A Safe Guide (2026)

June 23, 2026

To make water safe to drink at home in an emergency, the most reliable method is to bring it to a rolling boil for at least one minute. If you cannot boil it, use purification tablets or a certified filter, and always start from the clearest water you can find. Sweden's Agency for Civil Defence (MCF, formerly MSB) recommends every household be able to manage at least one week on its own, and water is the first thing to secure. Here is how to purify water safely, at home and on the move.

Reviewed by Oskar Bjork, defence engineer (Swedish Armed Forces) and adviser to Kapsel. Last updated 2026-06-23.

How to purify water at home

There are three methods that reliably make water safe to drink: boiling, purification tablets, and a certified filter. At home the simplest is usually boiling, because you can do it on any stove or camping burner. If the power is out, tablets and filters need no heat and store for years. Whichever you choose, start from the clearest water you can find and treat only water you actually need to.

How much water you need

Plan for at least 3 litres of drinking water per person per day, and 3 to 5 litres including hygiene. Over a week that is roughly 20 to 35 litres per person. Store as much as you reasonably can, and keep a way to treat more, because stored water runs out faster than people expect.

The three reliable methods

1. Boiling, the most reliable

Bring water to a rolling boil and keep it there for at least one minute (three minutes at high altitude).
Boiling kills bacteria, viruses and parasites. Let it cool and store it in a clean, covered container.
Boiling does not remove chemicals, fuel or heavy metals, so start from a clean source.

2. Purification tablets

Chlorine dioxide or chlorine tablets are compact and ideal when you cannot boil.
Follow the dose and the wait time on the pack, usually around 30 minutes, longer if the water is cold or cloudy.

3. A certified filter

A microbiological filter removes bacteria and protozoa. Check whether it also handles viruses if you need that.
Pre-filter cloudy water through a clean cloth first so the filter lasts longer.

Disinfecting water with chemicals

When you cannot boil, chemical disinfection is the compact backup. Purification tablets (chlorine dioxide or chlorine) are dosed for a known volume, so they are simpler and safer than measuring household bleach. Follow the pack: add the tablet, wait the stated time (usually around 30 minutes, longer if the water is cold or cloudy), and always disinfect the clearest water you have, because sediment and cloudiness protect microorganisms from the chemical.

Can you drink rainwater?

Freshly fallen rain is usually clean, but by the time it reaches you it has run across a roof, gutter or other surface and picked up dirt, bird droppings, and whatever the surface is made of. Treat collected rainwater the same as any other untreated water: let it settle, filter out debris, then boil it or use tablets before drinking. Do not drink rainwater collected from surfaces that may shed chemicals, and avoid the first run-off after a dry spell.

Start from the clearest water

Whatever method you use, begin with the cleanest water available. Let sediment settle and pour off the clear water, or strain it through a cloth. Cleaner input gives a safer result and makes filters and tablets work better.

Common mistakes to avoid

Treating water you do not need to. If the mains supply is still safe, use it.
Using water from pools, radiators, or anything that may contain chemicals or fuel.
Assuming boiling fixes everything. It kills microorganisms but does not remove chemical contamination.
Storing treated water in a dirty container, which can recontaminate it.

Want it all sorted at once?

Purifying water is one part of being ready. Kapsel Core covers a full week of water, warmth, light and first aid in one system, reviewed by a defence engineer and quality-checked in Sweden.

See Kapsel Core

Where this fits in your preparedness

Water is one of the five basics, alongside heat, light, communication and food. Build it into your kit from our complete emergency-kit checklist and plan your amounts with our food and water stores for a week. For the food side, light, long-life options like freeze-dried food pair well with treated water. The Kapsel Core covers water in its Water and Health capsule, with a filtered water bottle and purification tablets built in, so there is less to source and track. See the Kapsel Core.

Frequently asked questions

How do I purify water at home?

Bring it to a rolling boil for at least one minute. If you cannot boil, use purification tablets or a certified filter, and always start from the clearest water you can find.

How long should I boil water to make it safe?

Bring it to a rolling boil for at least one minute, or three minutes at high altitude. That kills bacteria, viruses and parasites.

Are water purification tablets safe?

Yes, when used as directed. Follow the dose and the wait time on the pack, and allow longer if the water is cold or cloudy.

Can you drink rainwater?

Freshly fallen rain is usually clean, but once it has run over a roof or gutter it can pick up dirt and contaminants. Let it settle, filter out debris, then boil it or use tablets before drinking.

Does boiling remove all contamination?

No. Boiling kills microorganisms but does not remove chemicals, fuel or heavy metals. Start from the cleanest source you can and avoid contaminated water.