Best Emergency Water Purification Method (9 Systems for Disaster Relief)

Having an effective water purification method is a critical part of disaster prepping. But it can be difficult to know which option to use.

There is a lot of information about water purification systems, and a lot of the info is purposely misleading because companies want you to buy their products.

The reality is that there is no “best” method of purifying water in disaster situations.

Which water purification method to use depends on your situation and the threats present.

For example, a water treatment system designed for backcountry use where viruses aren’t likely probably won’t be safe for treating floodwater in an urban environment.

Here is an overview of the 9 methods of disaster water purification and the pros/cons of each.

1. Boiling

Treats: Bacteria, Parasites, Protozoa, Viruses

Doesn’t Treat: Organic and Inorganic chemicals, Radionuclides

Boiling is a good way to treat water in most common disaster situations, such as grid outages when the water treatment center stops working.

Most sources (including FEMA and the Red Cross) say that you need to boil water for 1 minute to kill bacteria, viruses, parasites, etc.

Suitable for: Backcountry water, tap water during power outages


  • Kills most common threats
  • Easy to do
  • Requires time, heat, and fuel
  • Won’t remove chemical threats

2. Chemical Treatments

Treats: Bacteria, Parasites, Protozoa, Viruses

Doesn’t Treat: Organic and Inorganic chemicals, Radionuclides

The term “chemical” water treatment is a bit confusing, but these are some of the most common methods for treating contaminated water.

For example, you can buy water treatment tablets or drops to put in unsafe water to kill bacteria, parasites, and viruses.

The main downside of water treatment tablets is that they are limited in quantity. Where some water filters can be used for thousands of gallons, one tablet will usually only treat one liter of water.

Probably the most common chemical treatment for water is chlorine bleach.

Make sure it is unscented bleach with no added cleaners. It should say 8.25% sodium hypochlorite on the label.

To treat water with bleach, you’ll need to add 6 drops per gallon of water and let it sit for 30 minutes.

Suitable for: Backcountry water, tap water during power outages


  • Cheap and readily available
  • Kills most common threats
  • Portable
  • Doesn’t remove sediment from water
  • May create a bad taste
  • You have to let the water sit before using
  • Doesn’t remove chemical threats

3. Mechanical Filtering

Treats: Bacteria, Parasites, Protozoa, Inorganic chemicals, Viruses*

Doesn’t Treat: Organic chemicals, Radionuclides, Viruses*

*Check product specification

Water filters are considered a type of “mechanical” water treatment because they trap contaminants that go through them.

There is a lot of variability in water filters, so you must be careful when choosing one. The most important thing to look at is the micron size rating. This refers to the size of contaminants that the filter can remove.

The smaller the number, the better the filter will remove contaminants.

I suggest you read our reviews of some of the best survival water filters here for more information.

Bottom line: To safely treat bacteria, a water filter must filter at least 0.2 microns.

Using Water Filters on Viruses

Note that viruses are incredibly tiny, so most mechanical filters will not remove them.

Suitable for: Backcountry water, tap water during power outages


  • Many options available
  • Cheap
  • Portable
  • Not all products remove viruses
  • You may need to buy replacement filters
  • Not all filters are made equal

4. Activated Carbon Filtering

Treats: Organic chemicals, Some radionuclides

Doesn’t Treat: Bacteria, Parasites, Protozoa, Viruses, Inorganic chemicals

Activated carbon is a really interesting substance. Unlike the materials used in mechanical water filters, which “catch” impurities, activated carbon absorbs impurities.

This unique property makes activated carbon the only water treatment method that will remove organic chemicals such as benzene and pesticides.

I think that every person should have some activated carbon (Amazon Link) in their disaster supplies. However, it is vital for anyone living near industrial plants or agricultural areas.

While the activated carbon won’t kill bacteria, parasites, or viruses, it can be combined with boiling to make very-contaminated water safe for consumption.

For example, let’s say there has been a terrible hurricane and you don’t have any bottled water left. You could boil the flood water (which would kill viruses, bacteria, and protozoa/parasites) and then use activated carbon to remove the many toxic chemicals in the water.

You can even make your own activated carbon in a pinch.

Saturation Level

One important thing to note about activated carbon is its saturation level. At a certain point, it won’t be able to absorb any more impurities.

If you continue using the carbon filter after its saturation point, all those absorbed impurities will leach into the water. Unfortunately, it is tough to gauge when that saturation point has been reached.

The dirtier the water, the faster the carbon will become saturated.

Suitable for: Removing chemicals from toxic water (such as in floodwater, near industrial sites, or biochemical attacks), nuclear disasters.


  • One of the only systems to remove organic chemicals
  • Portable
  • Does not remove common threats like bacteria and parasites
  • Filter must be replaced regularly

5. UV Treatment

Treats: Bacteria, Parasites, Protozoa, Viruses

Doesn’t Treat: Organic and Inorganic chemicals, Radionuclides

Ultraviolet light causes the DNA in bacteria, viruses, and parasites/protozoa to scramble. They will still be in the water, but they will be harmless.

You can buy UV water treatment wands. To use them, you put the wand in the dirty water, push a button, and let the UV light do its work.

These methods are great because they are portable and kill viruses (which filtering does not do).

Some sources say UV treatment methods’ effects are only temporary because the DNA can become unscrambled. So, you should consume the treated water immediately instead of waiting hours after treatment.

UV water treatment systems rely on batteries, which could be a problem in specific disaster scenarios.

Suitable for: Backcountry water, tap water during power outages


  • Destroys common threats, including viruses
  • Portable
  • Doesn’t remove sediment
  • Requires a battery
  • Pathogens can reactivate if you let the water sit for a long time
  • Doesn’t remove chemicals

6. Reverse Osmosis

Treats: Bacteria, Parasites, Protozoa, Viruses, Inorganic chemicals, Some radionuclides

Doesn’t Treat: Most organic chemicals

Reverse osmosis systems are very complex and somewhat expensive. They work by hooking up to your water system and forcing pressurized water through a special membrane.

Reverse Osmosis System on Amazon.

When it comes to treating water, reverse osmosis is one of the most effective single methods. The only impurities the system won’t remove are organic chemicals (such as fluoride, chlorine, and lead).

However, because reverse osmosis systems are so costly, it is unlikely that anyone will want to rely on this method for emergency preparedness.

It is worth mentioning that reverse osmosis is the only method that will remove significant amounts of radioactive materials.

If you live near a nuclear facility, it might be worth the investment to get one of these systems.

Suitable for: Backcountry water, tap water during power outages, floodwater, nuclear disasters.


  • Very effective at purifying water
  • Hooks up to plumbing system, so won’t work when the water system is down
  • Wastes a lot of water
  • Expensive
  • Not portable

7. Distillation

Treats: Bacteria, Parasites, Protozoa, Viruses, Inorganic chemicals, Some radionuclides

Doesn’t Treat: Most organic chemicals

CNCShop Water Distiller Water Distillation Purifier All Stainless Steel Internal 4L Purifier Filter Effective

Most home water distillers work by boiling water and then collecting the steam. The steam is channeled into a separate container where the vapor cools and turns back into water. The idea behind distillation is that microorganisms and pollutants are left behind.

However, organic chemicals like pesticides and VOCs readily convert to vapor, so a distiller won’t remove these. However, most home distillation systems have special pre-filters to eliminate these threats.

You can have a look at a system on Amazon here.

Also, see does distilled water go bad?

Suitable for: Backcountry water, tap water during power outages, saltwater, floodwater, nuclear disasters.


  • Effective at removing most common threats
  • Requires electricity
  • Can take a while to treat water
  • Expensive

8. Ion Exchange

Treats: Inorganic chemicals, Some radionuclides

Doesn’t Treat: Bacteria, Parasites, Protozoa, Viruses, Organic chemicals

Without getting too technical, ion exchange water treatment systems rely on porous polymer beads. When water hits the surface of the beads, it causes a release of ions.

The result is that “bad” ions are exchanged for “good” ions.

Ion exchange systems don’t really purify water since they only remove heavy metals and some organic chemicals. Thus, they are considered water softeners.

But, if you are worried about arsenic, lead, mercury, or other toxic heavy metals in your drinking water, an ion exchange system would be good.

Suitable for: Situations where heavy metals might be present in the water, such as water systems fed by old lead pipes (think of the crises in Flint, MI, and Corpus Christi, TX).</em


  • Removes toxic heavy metals
  • Doesn’t remove common threats in emergency situations

9. Rainwater Collection

Treats: Bacteria, Parasites, Protozoa, Viruses, Inorganic chemicals, Some radionuclides

Doesn’t Treat: Most Organic chemicals

Rainwater catchment is a form of distillation since the sun evaporates the water into vapor, and then when it collects and cools in the sky, it comes back in the form of rain.

However, you don’t get a pre-filter with rain, so it could contain lots of organic chemicals (acid rain, anyone?).

You’ll also have to be careful about how you catch and store your rainwater so bacteria and mold don’t start to grow!

If you have no other way to treat water, though, in an emergency, rainwater is one of the cleanest, safest options (barring nuclear emergencies and chemical attacks).

Read more about rainwater collection.


  • No special equipment required
  • You can’t rely on it to rain
  • You have to catch and store the rain

Which Water Purification Method to Choose?

With so many water treatment methods, figuring out which one to use can be confusing.

You will need more than one method to make your water safe – and even that might not help you in certain crises such as biochemical attacks.

Here is an overview of what treatment methods you could use depending on the situation:

  • Backcountry Use: Because viruses and chemicals aren’t usually threats in backcountry water, you could use boiling, mechanical filters, chemical treatments, or UV water treatments to treat the water safely. Read about ways to purify river water.
  • Power Outages: During power outages, the water treatment facility might stop working, and bacteria, protozoa, and parasites become a risk. You could use boiling, mechanical filters, chemical treatments, or UV water treatments.
  • Flood Water: Because of how contaminated floodwater is with chemical runoff, sewage, and even dead bodies, it should never be consumed. However, if you have to drink flood water, you should first filter it AND then boil it AND then use activated carbon.
  • Salt Water: Distillation is the only way to treat salt water. You can make a solar still to do this. Read about making saltwater drinkable.
  • Chemical Spills or Chemical Attacks: In situations like fracking disasters or terrorist attacks on the water supply, you are best to rely on bottled water. If you must, use activated carbon to treat the water.
  • Nuclear Disasters: No method is going to help you completely. However, reverse osmosis is your best bet. If you don’t have this system, you can use activated carbon and/or distillation.

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Hopefully it will never come to this because you’ve got enough long-term emergency water stored to get you through a disaster, but you can never be too prepared!

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Leave a comment

    • You’d have to use a method which kills viruses, bacteria, parasites, and algae (so boiling, UV light or a really good filter that removes viruses) AND another method for removing chemicals which might be in the pool water (activated charcoal). Or just save the pool water for things like hygiene instead of drinking water.

      • Everything I’ve read suggests that water filters do not remove viruses; only purifiers do. Your statement suggests that “a really good filter [will] removes viruses. Which ones do that?

  1. One problem I have with most of the filter products are their claims. When I ask them for data to support their claims they do not have it.

  2. Hello Jacob, I am interested in purchasing some activated carbon to have on hand for water filtration as shown in the video. The two links you have to amazon seem to be for a very fine powder carbon and most reviews say it is too fine to use with a coffee filter. Do you have any other suggestion for a coarser ground activated carbon that would be suitable for this purpose. Thanks for all the great information !

    • Just about any coarser activated carbon from a reputable brand should be fine. Just be warned that the surface area will be less (compared to the same weight of finely-ground activated carbon). So, it will take longer for the carbon to do its job.

    • You can get coarse activated carbon at pet stores used for fish tank filtration. If you crush it a bit you’ll get more surface area for adsorption. AC doesn’t absorb things (take them inside itself), it adsorbs them by collecting them (adding) onto its surface. By crushing it, you give it more surface area to collect stuff.


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