Water Treatment: Boil vs Filter vs Chemical vs UV

Clean water is one of, if not, the most essential resources for survival. The average human can only last 3-5 days without the consumption of a hydrating liquid, though this can vary depending on health and environmental factors (activity level, heat, etc.)

When an emergency strikes, one of the first things you need to do after the dust settles is secure fresh drinkable water. Water found in nature from a pond, river, stream, etc. isn't always safe to drink how you find it. This in turn may create the need for you to treat water from questionable sources. Here's four different water treatment methods, how they work, and when to use them:

The Four Methods

1. Boiling

How it works: Heat water to a rolling boil and let boil for at least 1 minute (3 minutes or longer at high altitudes).

Pros:

• Kills bacteria, viruses, and parasites
• Minimal equipment needed (just a heat source and container for water)
• Simple, reliable and time-tested
• Can treat large amounts of water quickly

Cons:

• Requires fuel and time
• Doesn't remove chemical contaminants
• Doesn't improve taste or clarity
• Uses significant fuel
• Gives away position

Best for: Base camp situations, when you aren't likely to be on the go, and have a reliable fuel supply (propane, wood, etc.)

2. Filtration

How it works: Physical barrier removes particles, bacteria, and protozoa. Some filters also remove viruses.

Pros:

• Improves taste and clarity
• Fast and convenient
• No chemicals or fuel needed
• Some filtration systems offer long-lasting filters (100,000+ gallons)

Cons:

• Doesn't remove viruses (unless specifically designed)
• Can clog with sediment
• Requires maintenance
• Upfront cost

Best for: Backpacking, bug-out bags, and regular use.

Recommended Filters

3. Chemical Treatment

Disclaimer: I'm not a chemical engineer. Adding too much chemical treatment can be dangerous. Always follow manufacturer instructions carefully. Use chemicals at your own risk and consult professional guidance if uncertain.

How it works: Chemicals like chlorine dioxide or iodine added to water source kills pathogens.

Pros:

• Lightweight and portable
• Long shelf life
• Effective against viruses
• No fuel needed

Cons:

• It takes time (from 30 minutes up to 4 hours)
• Doesn't improve taste (in fact, it often makes it worse)
• Doesn't remove particles
• May not work in very cold or turbid water

Best for: Emergency backup, treating large quantities, or when other methods aren't available.

Common Options:

Note: Bleach (household, unscented) also works in a pinch. General rule of thumb: 2 drops per liter. Use at your own risk and follow proper dilution guidelines.

4. UV Purification

How it works: Concentrated UV light destroys the DNA of microorganisms.

Pros:

• Very fast (60–90 seconds)
• Effective against bacteria, viruses, protozoa
• No chemicals or fuel
• Compact devices available

Cons:

• Requires batteries or power
• Doesn't work in turbid water
• Doesn't improve taste
• Higher upfront cost
• Higher complexity to other methods

Best for: Travel, urban emergencies, or as a supplement to filtration.

Recommended UV Purifiers

Comparison Table

*Some filters remove viruses (e.g., MSR Guardian, LifeStraw Mission)

Best Practices

Pre-Filtering

Before any of the above treatment methods, if possible, pre-filter cloudy or sediment filled water:

• Use a bandana, coffee filter, shirt or cloth
• Let sediment settle
• Skim clear water from top

Combining Methods

If time allows, for maximum safety, combine multiple methods:

• Filter + Chemical: Filter first, then treat with chemicals
• Filter + UV: Filter for clarity, UV for viruses
• Filter + Boil (best taste): Remove sediment & cloudiness, then bring filtered water to a boil

Water Sources Priority

1. Best: Flowing water (streams, rivers)
2. Good: Clear standing water (lakes, ponds)
3. Avoid: Stagnant, smelly, or colored water
4. Never: Water near industrial areas or known chemical spills

Emergency Water Sources

• Rainwater (collect in clean containers)
• Snow and ice (melt first, then treat)
• Dew (collect with cloth)
• Plant transpiration
• Water from hot water tanks
• Water from toilet tanks (upper tank, not bowl, definitely not bowl….)

Storage

Before you start storing water, you need to know how much you'll need. Use our water needs calculator to determine the right amount for your household based on the number of people, activity level, and climate.

Store water in:

• Food-grade containers (BPA-free)
• Dark, cool location
• Rotate or re-treat every 6 months
• Label with date

Making the Decision

For 72-hour kits: Pack a filter (Sawyer Squeeze or LifeStraw) + chemical backup (Aquamira tablets)

For bug-out bags: Same as above, or upgrade to a gravity-based filter for base camp. (You should also have fire starters in your bug-out bag, making boiling a viable option)

Home preparation: Stock filters + chemical tablets + fuel for boiling. If you have a well, have a method to retrieve water from your well in the case of a power outage (manual well pumps are a great option). Brita water filters are also a great option, and great to use not in emergency situations as well.

For travel: Water bottle with built in filtration, basic water filter, + chemical backup

Final Thoughts

The best water treatment method is the one you have and know how to use. Always have a backup method. When in doubt, use multiple methods for maximum safety.

Also, make the time to practice with the methods you plan to use. Some are extremely straight-forward, some are a little more complex. Chances are, when you NEED to use one of these methods, it's going to be a stressful situation now. Do your future self a favor and become proficient today.

BLUF: No single method is perfect. Layer your defenses. Two is one, one is none.