To describe a simple water purification system.
Drinkable water must be free from impurities (clay, silt, algae), not too acidic (carbonic acid, sulphuric acid), and not too alkaline (lime, soda ash, sodium hydroxide). An inappropriate storage container can also contaminate the water; for example, if it contains lead.
Effective filtration involves passing the water through several layers of absorptive material such as sand, charcoal, and gravel to remove pollutants. The pH of the water can also be adjusted by adding acidic or alkaline material as needed to reach a neutral pH.
Microorganisms must also be removed or brought to safe levels by adding a chemical disinfectant, sufficient heating, or subjecting the water to ionising radiation.
Complex systems exist to filter large amounts of water for human consumption at scale, but following is a way to purify water at home with simple tools.
Deep groundwater is filtered naturally by the layers of sediment in the Earth. Basic filtration can mimic this process by layering a number of materials.
You will need:
This must be cleaned thoroughly before use. It helps to filter out the largest pollutant particles.
The best sand to use is very fine.
3. Activated charcoal
This can be obtained from a pet store. It is used in the filtration systems for fish tanks.
4. Cotton balls
Obtain from any pharmacy
5. Coffee filters
Normal store-bought filters.
6. A large plastic bottle
A large, round, 20-30 litre bottle. The larger, the better.
Follow these steps:
1. Cut the bottom off the plastic bottle and invert it.
2. Place the coffee filter at the bottom near the bottle neck.
3. Place the cotton balls next.
4. Place the activated charcoal.
5. Place the sand.
6. Place the gravel.
Place a receiving container below the inverted bottle neck to catch filtered water. Pour unfiltered water into the opening above the gravel and allow it to make its way to the bottom. Any receiving container should be thoroughly rinsed with soap and water before use.
Microorganisms can be removed by bringing the water to a rolling boil for 1 minute at any elevation below 2000 metres. Above 2000 metres, it should be boiled for 3 minutes.
Boiling can be done in a saucepan. Alternatively, a length of copper tubing can be linked to the bottom of the layered filter and brought in to contact with a heating element such as an open flame or an electrical resistance coil. The copper tubing should itself be coiled around the element to allow water that passes through it to have sufficient exposure to the heat. Water can then be collected once it has passed through the tubing.
Once water has been purified, it is important to store it properly to avoid re-contamination. This can done in large plastic drums in a sheltered place. Tap water from the mains can also be stored this way. It is treated with chlorine to prevent growth of biological contaminants, but purified water from other sources will need chlorine added. This can be done by means of chlorine tablets or powder.
Recommended chlorine levels for human consumption are below 4 parts per million. This corresponds to up to 4 milligrams per litre of water. Unless the volume of water is very large, this will require a very sensitive scale to measure.
Storage can be done in any container that is sufficiently inert to avoid contamination, such as plastic. Smaller water containers can be used if the seal is airtight.
Polyethylene plastic containers are the most suitable container currently available and are recommended for long-term storage. A chemical called Bisphenol A, or BPA, is sometimes used a sealant on these containers. Some research suggests that it can interfere with prostate function in infants, but it is widely agreed to be safe in small amounts. BPA-free containers are widely available.
Water that has been stored for a long time can often taste "stale". This is primarily due to low levels of oxygen and can be resolved by stirring the water to aerate it.
1. Large plastic water drums in a sheltered place.
2. Chlorine powder or tablets.
3. A scale sensitive to 1 milligram accuracy.
Note: Copies of relevant source material have been stored at:
Source material: A simple water purification system