Filtering water with rocks and sand can be an interesting experiment. Just because the water may seem clear to the naked eye does not mean it is potable and should be ingested. In fact, you should not drink the water you use in this experiment. As you probably know, water does not come right from the ground ready to drink. There are many particles and impurities in the water. Before being sold to us it goes through rigorous filtering systems.
Many of these particles are large enough that we can filter them out with rocks and sand. But as previously stated, there are still microscopic particles that will not be filtered out through this crude filtration system and the water should not be consumed.
To conduct this experiment you’ll need a few items:
- Utility knife/scissors
- Two plastic water bottles
- Rubber band
- Coffee filter
First you’ll want to cut the bottom, about 4 inches, off of one of the water bottles. Remove the cap and attach a coffee filter to the outside of the bottle using a rubber band. On the second water bottle you are going to want to cut about four inches off of the top of the bottle. Take the first bottle (the one with the coffee filter) and insert it neck first into the second bottle.
The top bottle will act as the filter and the lower bottle will act as the water collector. If you happen to have beakers laying around you can use them instead of the water bottles.
To create the filter you will start by pouring small rocks, or gravel, into the bottle opening. The coffee filter will restrict it from going into the bottle neck. Next, you’ll pour sand on top of the gravel. If possible, use two types of sand – large grain and fine grain. The fine grain should go on last to create a layering effect.
Finally you will add your water. It’s best to first clean your filter with regular tap water. This will remove any dirt particles on the rocks. Be sure to pour carefully as to not disturb the sand too much. Once the tap water is completely through the filter you can pour it out of the water collection bottle.
Use dirty water to see how effective your rock filter is. Let the dirty water drain through the rock filter completely. You’ll see the difference in clarity once the water is collected in the second bottle.
Although this may be a fun and interesting experiment you should not rely on this method in a survival situation. You can not be sure that microscopic particles and impurities have been filtered thoroughly. Drinking impure water can lead to illness or death.