How to filter water in the wild

One of the most common problems people encounter when finding themselves in a survival situation is running out of water. Unless you’re in the desert or somewhere very hot, water will likely be very close, but it could also contain harmful parasites and bacteria that could make your situation much worse. It’s too dangerous to risk drinking straight from a natural water source, especially in certain areas, and instead, the water needs to be filtered and treated first. Here are the most common methods of how to filter water in the wild.

1. Boiling

Boiling is one of the most effective and straightforward ways to purify water in the wild. It kills bacteria, viruses, and parasites that can cause waterborne diseases. It is the easiest and most certain way of making sure that whatever is living in the water doesn’t make it through the boiling process.

(Boiling is the single most effective way to make water safe, even if it contains small pieces, the harmful bacteria and parasites will still be killed)

How to Do It:

• Collect water from a stream, lake, or other water source.
• Strain the water through a cloth or bandana to remove debris like leaves or dirt.
• Place the water in a metal container or heat-resistant bottle.
• Boil the water for at least 3 minutes, depending on your altitude. In higher altitudes (over 6,500 feet), boil the water for at least 5 minutes to account for the lower boiling point of water.
• Let the water cool before drinking.

Pros:
Highly effective at killing pathogens.

Works without the need for specialized equipment.

Cons:
Requires a heat source and a container, and doesn’t remove chemical pollutants.

2. Portable Water Filters

Portable water filters are lightweight and convenient devices designed for backpackers and survivalists. They usually come with a pump, straw, or squeeze mechanism and use a physical filtration system to remove contaminants.

(most manufacturers claim their portable water filters remove 99.99% of bacteria and can process around 3000 liters of water)

How It Works:

• Most portable filters use a combination of ceramic or fiber membranes that physically remove bacteria, protozoa, and microplastics.
• Some advanced filters may also incorporate activated charcoal to reduce chemicals and improve taste.
• Simply place the intake hose in the water source and pump or sip water through the filter.

Pros:
Removes most pathogens and sediments; fast and portable.

Cons:
Filters may clog over time, and they don’t remove viruses unless specifically designed to do so.

3. UV Water Purification (Steripen)

Ultraviolet (UV) purifiers, like the Steripen, use UV light to disinfect water by destroying the DNA of harmful microorganisms, rendering them unable to reproduce.

How It Works:

• Collect water in a clean container.
• Activate the UV device and stir it in the water for 45 seconds to 1 minute.
• The UV light kills bacteria, viruses, and parasites.

Pros:
Quick, effective, and lightweight.

Cons:
Requires batteries, doesn’t remove sediment, and doesn’t work well in cloudy or turbid water unless pre-filtered.

4. Water Purification Tablets

Water purification tablets are a lightweight and compact option for treating water in the wild. They typically contain chlorine, iodine, or chlorine dioxide, which disinfect the water by killing harmful organisms.

(Water purification tablets do an excellent job at making water safe and take up little space in a backpack, but they leave a noticeable taste in the water)

How to Use:

• Fill a container with water.
• Add the recommended number of tablets based on the water volume.
• Let the tablets dissolve and wait for 30 minutes to 4 hours, depending on the type of tablet and water temperature.
• Stir the water or shake the bottle to ensure even distribution.

Pros:
Lightweight, portable, easy to store, and effective against most pathogens.

Cons:
Can leave an unpleasant taste, and effectiveness may vary with temperature or water clarity.

5. Gravity Water Filters

Gravity water filters use the natural force of gravity to push water through a filtration system. They typically consist of two chambers: one for dirty water and one for filtered water. Water moves from the top chamber through a filter and collects in the bottom chamber.

(Gravity water filters are a good option for anyone who isn’t in a rush, or for an over-night resupply)

How It Works:

• Fill the top reservoir with unfiltered water.
• Let gravity pull the water through the filtration medium, which removes impurities and pathogens.
• Collect the filtered water from the lower chamber.

Pros:
Great for filtering large amounts of water without requiring physical effort.

Cons:
Slower than other filtration methods, and filters can clog with time.

6. Improvised Sand and Charcoal Filter

In a survival situation without access to modern filtration tools, you can make a DIY filter using materials from your surroundings, such as sand, charcoal, and pebbles. This method helps remove debris and improve the clarity of the water, but it doesn’t kill pathogens, so it should be combined with boiling or chemical treatment.

(This type of filter does a great job at removing bits from the water, but does little to remove the harmful micro-organisms)

How to Make It:

• Use a container like a plastic bottle or hollowed-out wood.
• Layer small pebbles, sand, and activated charcoal in the container. Start with pebbles at the bottom, then sand, and finish with charcoal.
• Pour the collected water through the filter.
• The layers will remove dirt and some impurities, but it’s essential to boil or chemically treat the filtered water afterward.

Pros:

Can be made with natural resources in an emergency.

Cons:

Only removes physical impurities and does not purify the water from bacteria or viruses.

7. Solar Water Disinfection (SODIS)

Solar Water Disinfection (SODIS) is an energy-efficient method that uses sunlight to kill bacteria and viruses in water. This technique is simple but can take hours to work.

(Pet stands for Polyethylene terephthalate, which is just a type of food-grade plastic safe for storing consumable products)

How to Do It:

• Collect clear water in a transparent plastic bottle or bag.
• Place the container in direct sunlight for at least 6 hours (or 48 hours if it’s cloudy).
• The UV rays from the sun will disinfect the water, making it safe to drink.

Pros:
Requires no specialized equipment and is free.

Cons:
Time-consuming and only works with clear, shallow water. Not effective for highly contaminated water.

8. Cloth Filtering

If you are left with no other tools, filtering water through a cloth can remove large debris and particles. While this method doesn’t purify the water, it helps improve the water’s clarity and removes sediment.

How It Works:

• Pour water through a clean cloth, bandana, or shirt into a container.
• Once the water is filtered for debris, it should be boiled or treated with tablets for further purification.

Pros:
Easy to implement with basic supplies.

Cons:
Does not remove harmful microorganisms or chemicals.

A word of Caution on how to filter water in the wild

There will hopefully be very few situations where you need to know how to filter water in the wild, but this should only be done when you have no other choice. Know that micro-organisms are only possible to filter out with a professional filter, and the homemade filters or something you can put together in the woods will only remove bits from the water and not the nasty creatures that can cause a wide range of illnesses. If you don’t have something to kill the bacteria like purification tablets or a device like the Steripen, then you MUST boil the water to make it safe before drinking.