In an emergency, tap water may stop flowing or become unsafe because floods, broken pipes, or power outages can let germs and chemicals enter the water supply. Safe drinking water matters because dehydration can become dangerous quickly, but contaminated water can cause serious illness. Emergency water purification is the process of making the safest possible water using steps such as settling, filtering, disinfecting, and storing it properly.
Students should learn these steps before an emergency because clear water is not always safe water.
Key Facts
- First remove visible dirt by settling and filtering, then disinfect the water to kill germs.
- Boiling is one of the safest emergency methods: bring water to a rolling boil for 1 minute, or 3 minutes above 2,000 m elevation.
- If using unscented household bleach at 5 percent to 9 percent sodium hypochlorite, add 2 drops per 1 L of clear water, stir, and wait 30 minutes.
- For cloudy water treated with bleach, filter it first if possible, then use 4 drops per 1 L and wait 30 minutes.
- Volume conversion: 1 gallon = 3.785 L, so an emergency supply should include about 3.8 L per person per day.
- Disinfection kills many microbes, but it does not reliably remove chemicals, salt, heavy metals, or fuel contamination.
Vocabulary
- Purification
- Purification is the process of making water safer to drink by removing particles and reducing harmful contaminants.
- Filtration
- Filtration is the process of passing water through a material that traps dirt, sediment, and some microbes.
- Disinfection
- Disinfection is the step that kills or inactivates disease causing organisms such as bacteria, viruses, and parasites.
- Pathogen
- A pathogen is a microorganism that can cause disease, such as certain bacteria, viruses, or protozoa.
- Rolling boil
- A rolling boil is vigorous bubbling across the entire surface of the water that does not stop when stirred.
Common Mistakes to Avoid
- Drinking clear-looking water without disinfecting it is unsafe because many dangerous pathogens are invisible.
- Filtering muddy water and assuming it is fully safe is wrong because filtration removes particles but may not kill viruses or bacteria.
- Using scented bleach, splashless bleach, or cleaners with additives is dangerous because those products can contain chemicals not meant for drinking water.
- Storing purified water in a dirty container can recontaminate it because germs from the container can enter water that was already treated.
Practice Questions
- 1 A student has 6 L of clear emergency water and 5 percent to 9 percent unscented household bleach. Using 2 drops per 1 L, how many drops of bleach are needed?
- 2 A family of 4 wants a 3 day emergency water supply. Using 3.8 L per person per day, how many liters should they store?
- 3 A flood leaves water that smells like gasoline. Explain why boiling or adding bleach is not enough, and describe the safest decision the family should make.