Few things in life are more important than having a supply of clean, fresh, pure, and safe drinking water. A solar distillation system is a great option and we will investigate that in a future post. For now, let’s explore another approach that uses no moving parts… a filter.
The filter I’m about to describe will provide water at least as good as the venerable Berkey but much more cheaply and without the cost of expensive cartridge replacements. It’s based on the one shown here in this video.
As good as that seems, I need to advise caution before using just any clay pot. While natural clay is rarely seriously contaminated with heavy metals, the processing and handling of terra cotta pots can sometimes render them unsuitable for use as water filters.
I recommend you look for a pot made in Italy and avoid anything from China or the Middle East.
Warning: Before using your terra cotta pot, cleanse and/or test it for heavy metals such as lead. Contaminated pots can leach harmful substances into the filtered water. Follow the procedure outlined below to test the pot for contaminants.
If you’re not sure of the quality of the clay pot material, I would strongly advise to pre treat it twice with hot cleaning vinegar. White vinegar has 5 percent acidity; while cleaning vinegar, on the other hand, has 6 percent. Although it’s only a one percent difference in acidity, it actually results in a 20 percent difference in strength.
Decontaminating Your Pot
Make sure the drainage hole is plugged with a cork and/or paraffin wax. Fill your pot to the top with your hot vinegar solution and let it weep through the clay. The reason for this is that acetate ions will bind to most heavy metals that may be in the clay. All acetates are water soluble (or most – if memory serves correctly) and the most toxic metals will form acetates, so this would take care of free floating microscopic metal bits, for the most part. Then run 2-4 potfuls of plain hot water through to wash out the acetates (could take all day). The main thing is to try to leach out all the lead from the clay.
Testing Your Terra Cotta Pot
In the end, the only way to know for certain that your pot is acceptable is to test it. The simplest way is to purchase a kit like this one. Fill your pot with distilled water and let it soak for several hours. You may want to place it in a clean glass or plastic tub to expose the outside to the water. After some time, use your test kit to check the leachate. Do not use that pot until after the vinegar cleansing process can be done successfully and the test passes.
If you’re more of a DIY kinda person, try adding 1 gram of Sodium Hydroxide (NaOH) or Potassium Hydroxide (KOH) to 10 ml of your leachate in a glass tube or beaker. The exact measures are not super critical. What is important however is your safety. Be sure to wear gloves and googles. Handle the hydroxide with care.
Add a few milligrams of pure Sulfur to your solution and slowly heat it. Let it boil for a few minutes. If you observe a black or dark gray precipitate, do not use that clay pot. This is the classic Sodium Sulfide Lead test. In the presence of Lead, black Lead Sulfide will drop out of solution. Please note that it is possible to get a false positive. If copper, nickel, iron, mercury, cobalt or cadmium are present, you will get a similar dark color change reaction. Forget what I said about a false positive. If your solution turns black you can be sure you are dealing with some type of heavy metal contamination. Regardless of the exact species, you don’t want to use that pot for drinking water.
Building a Water Filter Using Terra Cotta Pots
Once you have found the pot you want to use (8” is probably a good size for the suggested sun tea jar), it’s time to start building.
Materials List
- 1-2 gallon glass jar
- Non-glazed terra cotta pot to fit
- Fine sand
- Activated charcoal
- Small pebbles (half inch)
- Rusty nails (optional)
Assembling the Filter
- Prepare the Pot:
- Ensure it is free from cracks and damage.
- Clean the terra cotta pot thoroughly with water. Ensure it is dry before use.
- be sure to seal the bunghole.
- Small Pebbles:
- Add a layer of small pebbles to the bottom of the pot. This layer will help with drainage and keep the finer materials from clogging the exit holes.
- Activated Charcoal:
- Add a layer of activated charcoal on top of the small pebbles. Charcoal helps in removing impurities, odors, and some chemicals from the water.
- Fine Sand:
- Add a layer of fine sand on top of the carbon. Sand helps in filtering out smaller particles and debris from the water.
- More of the Same :
- Add alternate layers of charcoal and sand until the pot is nearly full.
- Rusty Nails:
- Mix a handful rusty nails into the last layer of sand. The iron oxide from the rusty nails will adsorb arsenic from the water, making it safer to drink.
- Top Layer of Small Pebbles:
- Add another layer of small pebbles on top of the sand. This will prevent the sand from moving around when water is poured in.
Using the Filter
- Position the Filter:
- Place the assembled terra cotta pot on top of the glass jar. Ensure it is stable and securely positioned inside the mouth of the jar.
- Fill with Water:
- Pour water into the pot, allowing it to percolate through the layers of pebbles, sand, charcoal, and rusty nails.
- Collect Filtered Water:
- Collect the filtered water in the glass jar. The water should be clear and free from larger particles.
- UV Sterilization (optional):
- Solar water disinfection (SODIS) is one of the cheapest and most suitable treatments to produce safe drinking water at the household level.
- Expose the glass jar to direct sunlight for at least 6 hours or 48 hours in cloudy weather to allow UV rays to sterilize the water, killing any remaining pathogens.
- The SODIS method should not be used at all in constant rainy conditions.
Maintenance
- Regular Cleaning:
- Periodically clean the layers to prevent clogging. Remove and replace the sand, charcoal, and rusty nails as needed to maintain filter efficiency.
- Check for Contaminants:
- Regularly test the filtered water for contaminants to ensure it remains safe for use.
By following these steps, you can build an effective water filter using a terra cotta pot, ensuring the removal of heavy metals and sterilization of the water. Always ensure the materials used are safe and free from contaminants to maintain the quality of the filtered water.