How to Filter Water for Cholera

by

In the face of a cholera outbreak, access to safe, clean water is not just a convenience—it’s a matter of survival. The bacteria that cause cholera, Vibrio cholerae, are predominantly waterborne. This makes the ability to effectively filter and purify water a critical, life-saving skill. This guide cuts through the noise, providing a direct, no-nonsense roadmap to securing a safe water supply for you and your family. We’ll focus on practical, actionable steps you can take right now, using readily available methods and materials.

The Immediate Priority: Your Action Plan

Before diving into the specifics of each method, let’s establish a clear, tiered action plan. When you’re in a situation where water contamination is a threat, you need to act fast.

  1. Assess Your Resources: What materials do you have on hand? Do you have access to a stove, a heat source, or chemical disinfectants? Do you have any commercial filters or water purification tablets?

  2. Choose Your Primary Method: Based on your resources, select the most effective and reliable purification method available to you. Prioritize boiling, as it’s the most foolproof.

  3. Implement a Backup Plan: Never rely on a single method. If your primary method fails or becomes unavailable, you must have a secondary plan ready to go. This could mean having a supply of purification tablets if your fuel for boiling runs out.

  4. Establish a Routine: Make water purification a daily, non-negotiable routine. Don’t wait until you’re thirsty. Purify water in batches so you always have a safe supply ready to drink.

The Gold Standard: Boiling Water

Boiling is the most effective and simplest way to kill Vibrio cholerae. The heat destroys the bacteria, making the water safe to drink. This method is accessible to almost anyone with a heat source.

How to Do It:

  1. Source the Water: Collect water from the clearest, most accessible source you can find. While boiling will kill the bacteria, you still want to start with water that is as clean as possible to reduce particulate matter.

  2. Bring to a Rolling Boil: Pour the water into a pot or kettle and place it over your heat source. A rolling boil is when large bubbles are consistently and rapidly breaking on the surface of the water.

  3. Maintain the Boil: Let the water continue to boil for at least one minute. If you are at a high altitude (above 6,500 feet or 2,000 meters), boil for a minimum of three minutes.

  4. Cool and Store: Remove the pot from the heat and allow the water to cool naturally. Do not add ice or anything else to cool it down, as this could re-contaminate the water. Store the cooled, boiled water in a clean, covered container.

Example:

Imagine you have a family of four and need 8 liters of water per day. You find a nearby stream. You would collect 8 liters of this water in a clean bucket. You have a 2-liter pot and a gas stove. You would boil the water in four separate batches. For each batch, you’d bring the 2 liters to a rolling boil and let it continue for one minute. After each batch cools, you would pour it into a sanitized, sealable container. This ensures you have enough safe water for the day’s needs.

Advantages: Extremely effective, simple, and requires no special equipment beyond a heat source and a pot.

Disadvantages: Requires fuel or electricity, and can be time-consuming. It does not remove chemical contaminants or heavy metals.

The Chemical Solution: Disinfection with Bleach or Iodine

If you don’t have a heat source or the means to boil, chemical disinfection is your next best option. This method uses common household chemicals to kill the bacteria.

Using Household Bleach

Only use plain, unscented household bleach with an active ingredient of sodium hypochlorite. The concentration is key, and it’s typically around 5-9%. Check the label.

How to Do It:

  1. Know Your Ratios: For clear water, use 5 drops of bleach per gallon (or 16 drops per 5 gallons). If the water is cloudy, double the amount of bleach. A medicine dropper is ideal for measuring.

  2. Add and Stir: Add the appropriate amount of bleach to your water container. Stir or shake the container thoroughly for at least 30 seconds to ensure the bleach is evenly distributed.

  3. Wait: Let the water stand for at least 30 minutes. You should be able to smell a faint chlorine odor. If you can’t, repeat the dosage and let it stand for another 15 minutes.

  4. Store: Once the 30-minute waiting period is over, the water is safe to drink. Store it in a clean, covered container.

Example:

You have a 5-gallon water jug of moderately clear water. The bleach you have is 6% sodium hypochlorite. You would add 16 drops of bleach to the 5-gallon jug. After sealing the jug, you would shake it for 30 seconds and then set it aside. You’d set a timer for 30 minutes. After the time is up, you would check for the chlorine smell. If it’s present, the water is ready to use.

Using Tincture of Iodine

Iodine is another effective disinfectant. Use a 2% tincture of iodine solution, which is commonly available in pharmacies.

How to Do It:

  1. Measure: For clear water, add 5 drops of 2% tincture of iodine per quart (or 10 drops per gallon). For cloudy water, double the dosage.

  2. Mix and Wait: Stir the water well after adding the iodine. Let it stand for at least 30 minutes.

  3. Taste and Store: The water will have a distinct taste. Once the waiting period is over, it is safe to drink. Store in a clean, covered container.

Advantages: Requires no heat, making it ideal for on-the-go situations. Effective at killing bacteria and some viruses.

Disadvantages: Can leave an unpleasant taste. Bleach degrades over time, so check the expiration date. It’s not as effective against all parasites and cysts.

The Physical Barrier: Filtration

Filtration is a crucial step, especially when dealing with visibly dirty or turbid water. It removes suspended solids, sediments, and can also remove larger microorganisms. However, filtration alone is often not enough to eliminate Vibrio cholerae, which are small enough to pass through many filter membranes. Therefore, filtration should always be followed by another purification method, like boiling or chemical disinfection.

Using a Commercial Water Filter

Commercial filters come in many forms, from simple straw filters to complex pump systems. Look for filters certified to remove bacteria. The pore size is the most important factor. To remove Vibrio cholerae, you need a filter with a pore size of 0.2 microns or smaller.

How to Do It:

  1. Source and Pre-Filter: Find your water source. If the water is very cloudy, consider a simple pre-filtration step. Pour the water through a coffee filter, a clean cloth, or layers of sand and gravel to remove large particles. This will extend the life of your commercial filter.

  2. Follow Manufacturer Instructions: Every filter is different. Read the instructions carefully. Some require pumping, while others work with gravity.

  3. Post-Filter Purification: After running the water through the filter, it is highly recommended to boil the filtered water or treat it with a chemical disinfectant as an extra layer of protection.

Example:

You have a pump-style filter with a 0.1-micron ceramic element. You’re at a lake with murky water. You would first scoop the water into a container. You’d take a clean t-shirt and stretch it over the mouth of another container, pouring the murky water through it to catch the worst of the sediment. Then, you’d use the pump filter to draw the pre-filtered water through the ceramic element into a final, clean container. Even with this filter, as a safety measure, you would then add the appropriate amount of bleach and let it sit for 30 minutes before drinking.

DIY Sand and Gravel Filter

In a pinch, you can create a makeshift filter to remove sediment. This method is for pre-filtration only and is not a substitute for boiling or chemical treatment.

How to Do It:

  1. Gather Materials: You’ll need a large, empty container (like a plastic bottle with the bottom cut off), a clean cloth or coffee filter, and layers of gravel, sand, and charcoal if available.

  2. Layer the Materials: Place the cloth at the bottom of the container. Add a layer of large gravel, followed by a layer of fine gravel, then a layer of coarse sand, and finally a layer of fine sand. If you have charcoal, a layer of crushed charcoal between the sand layers can help.

  3. Filter the Water: Pour the dirty water slowly through the top layer of sand. The water will drip out of the bottom of the container, much clearer than it was before.

  4. Purify the Filtered Water: This water is not safe to drink. You must now boil it or treat it with bleach or iodine.

Advantages: Removes large particles, improving the taste and clarity of the water. Prolongs the life of commercial filters.

Disadvantages: Does not remove bacteria. Can be time-consuming and labor-intensive to build.

The Sun’s Power: Solar Disinfection (SODIS)

Solar Disinfection (SODIS) is an effective and cost-free method that uses the sun’s ultraviolet (UV) radiation to kill bacteria, viruses, and parasites in water. It is a simple, passive method that is highly effective under the right conditions.

How to Do It:

  1. Choose the Right Container: You need clear, clean plastic bottles (PET bottles) with a capacity of 1-2 liters. The bottles should be free of scratches and colored labels.

  2. Fill the Bottle: Fill the bottle with the clearest water you can find. It’s best to pre-filter the water to remove any turbidity, as the sun’s UV rays cannot penetrate cloudy water effectively. Leave about 2 inches of air at the top.

  3. Shake and Lay Out: Put the cap on and shake the bottle vigorously for at least 30 seconds to aerate the water. This adds oxygen, which helps the disinfection process. Lay the bottles horizontally on a dark surface (like a black piece of cloth or a corrugated metal sheet) to maximize the surface area exposed to the sun’s rays.

  4. Wait for the Sun: The bottles must be exposed to full sunlight for at least 6 hours on a sunny day. On a partly cloudy day, you need to extend this time to two consecutive days. If it’s a very cloudy day, this method is not recommended.

  5. Ready to Drink: Once the exposure time is complete, the water is safe to drink directly from the bottle.

Example:

You’re in an area with plenty of sun but no access to fuel for boiling. You collect a few clear, 1-liter plastic bottles. You pre-filter murky river water through a clean cloth and fill the bottles. You place them on the ground on a black tarp in direct sunlight. You do this at 9 a.m. on a sunny day. By 3 p.m., the water has been disinfected and is safe to drink.

Advantages: Free, environmentally friendly, and requires no special equipment other than clear plastic bottles and sunlight.

Disadvantages: Requires at least 6 hours of strong sunlight, making it unreliable on cloudy days or at night. It is not a rapid solution.

Beyond the Basics: Combining Methods for Maximum Safety

The most secure way to ensure your water is safe is to use a combination of methods. This multi-barrier approach provides redundancy and confidence.

The Ultimate Protocol:

  1. Pre-filter: Run your water through a simple cloth or a DIY sand filter to remove large particles.

  2. Commercial Filtration: Use a certified water filter with a pore size of 0.2 microns or less to remove bacteria and other microorganisms.

  3. Boil or Disinfect: Boil the filtered water for one minute, or treat it with bleach or iodine.

  4. Store Safely: Transfer the purified water into a clean, airtight container.

This layered approach guarantees that even if one step is not 100% effective, the subsequent steps will handle the remaining threats. It’s the most responsible and effective way to secure a safe water supply.

A Final Note on Storage and Handling

Purifying your water is only half the battle. Storing and handling it correctly is just as important to prevent re-contamination.

  • Use Clean Containers: Ensure any container you use for storage is thoroughly cleaned and sanitized.

  • Keep Containers Covered: Always keep your stored water in a container with a tight-fitting lid to prevent dust, insects, and other contaminants from getting in.

  • Use a Clean Ladle or Spout: Avoid dipping your hands or dirty cups into the clean water. Use a clean ladle, or better yet, a container with a spigot.

  • Designate a Separate Water Source: Designate one container solely for purified drinking water. Do not use this water for washing hands, dishes, or anything else.

By following these practical and direct steps, you can create a dependable system for providing your family with safe drinking water, even in the most challenging of circumstances. Focus on what you can control, act with purpose, and make water purification a non-negotiable part of your daily routine. Your health and safety depend on it.