How to make water safe: a practical guide

Boiling, tablets, filters, sunlight. A guide based on official advice. The same text is in the free SurvivalZone app and works without internet.

First

1. Use the cleanest water you have: rainwater, tap water after an outage, a spring. Avoid standing water near roads, fields and factories.
2. Strain cloudy water through a clean cloth, a coffee filter or several layers of kitchen paper, then let it settle for 30 minutes.

Methods

1. Boiling: bring to a rolling boil and keep it boiling for at least 1 minute. The most reliable way to kill bacteria, viruses and parasites.
2. Water purification tablets: dose and wait exactly as the manufacturer says.
3. Unscented household bleach, plain sodium hypochlorite (about 5–6%): 2 drops per litre, stir and wait 30 minutes. The water should smell slightly of chlorine. Double the dose if it is cloudy.
4. Camping filter: removes bacteria and parasites but usually not viruses. Best combined with boiling or tablets.
5. Sunlight (SODIS method): a clear PET bottle up to 2 litres, clear water, 6 hours in full sun or 2 days if cloudy.

Storage

1. Keep treated water in clean, closed containers in a cool, dark place.
2. Stock: 3 litres per person per day, for at least 3 days.

Watch out

• Boiling and tablets do not remove chemicals, fuel or heavy metals. Do not drink water that smells or looks like that.
• Avoid flood water, even boiled, if you have any other option.

Keep it on your phone

SurvivalZone is a free app for every emergency, with no account and no app store. It works without internet and shows the nearest shelters and help points, local radio, a 72-hour plan and a mountain trip planner.

Other guides

• 🍲 Food without power
• ⛺ Shelter at home and outdoors
• 👨‍👩‍👧 Protecting your family and yourself
• 💊 Run out of medicine

All scenarios →

Sources

• WHO: water, sanitation and hygiene in emergencies
• BBK guide "Vorsorgen für Krisen und Katastrophen" (Germany)
• Polish government safety guide (MON, MSWiA, RCB, 2025)

Official sources are checked automatically every day. Last check: 2026-10-18.

General guidance only; it does not replace the emergency services. If a life is in danger, call 112.