Alum can be used to purify water by causing suspended particles to clump together and settle out. This process is called flocculation. Here's how to use alum effectively:
Steps for Water Purification with Alum:
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Collect Water Sample: Obtain the turbid or muddy water you wish to purify.
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Dosage: Use approximately one teaspoon (5 grams) of alum powder per 20 liters (about 5 gallons) of water. This ratio may need adjustment depending on the initial turbidity of the water. Start with a small amount and increase if needed.
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Dissolve the Alum: In a separate, clean container, dissolve the measured amount of alum powder in a small quantity of clean water. Stir until the alum is completely dissolved.
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Add Alum Solution to Water: Pour the dissolved alum solution into the turbid water you want to purify.
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Stir Thoroughly: Stir the mixture vigorously for 1-2 minutes to ensure the alum solution is evenly distributed throughout the water. This helps the alum particles to come into contact with the suspended impurities.
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Allow to Settle: Let the water stand undisturbed for at least one hour, or preferably several hours (e.g., overnight). During this time, the alum will cause the suspended particles (silt, clay, organic matter) to clump together into larger, heavier particles called "floc." These floc particles will then sink to the bottom of the container due to gravity. You will visually notice the water becoming much clearer as the particles settle.
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Carefully Decant/Filter: Once the sediment has fully settled, carefully pour the clear water from the top of the container into a separate, clean container, being careful not to disturb the sediment at the bottom. You can also use a clean cloth or filter to further filter the water as you pour it to remove any remaining fine particles.
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Boil or Disinfect (Important): Alum treatment clarifies water but does NOT disinfect it. After clarification, it is crucial to further treat the water to kill any remaining bacteria, viruses, or other pathogens. The most effective methods include:
- Boiling: Bring the clarified water to a rolling boil for at least 1 minute (or 3 minutes at higher altitudes).
- Chlorination: Use household bleach (unscented, containing 5.25-8.25% sodium hypochlorite) at a ratio of approximately 2 drops per liter of water. Stir well and let stand for at least 30 minutes before use. The water should have a slight chlorine odor.
- Solar Disinfection (SODIS): Fill a clear plastic bottle (PET) with the clarified water and expose it to direct sunlight for at least 6 hours.
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Store Properly: Store the purified and disinfected water in clean, sealed containers to prevent recontamination.
Important Considerations:
- Alum is most effective for removing suspended solids. It does not remove dissolved chemicals or heavy metals.
- The effectiveness of alum treatment depends on the type and concentration of impurities in the water.
- Always use food-grade alum if possible.
- Alum can slightly lower the pH of water. In some cases, adding a small amount of baking soda can help to neutralize the pH. However, this is generally not necessary.
- Alum treatment alone does NOT make water safe to drink. You must disinfect the water after using alum.
