Build your own water filter

We all know the water we usually drink is collected from lakes, rivers and other natural places. Therefore it must be extremely well “filtered” before people can drink it without any disease risk. This filtering process is in fact represented by several steps that water passes from lake water to clean water.

We will try to simulate the water purification process, but we won’t be using any harsh chemicals therefore the water we will obtain will not be safe for drinking. In order to start building your water purification system you will need several objects and some “dirty” water :
  • 2 liters of “dirty” water (from a lake, a swamp, any water older than 1 week or take some clear water and add some dirt to it),
  • 1 bottle (two liter bottle),
  • 2 more bottles (1 with the top removed the other with the bottom removed),
  • a recipient big enough for the “dirty” water,
  • 2 tablespoons of ALUM (Potassium Aluminum Sulfate – from a grocery store, it is known as “salt”),
  • sand (1+1/2 cups of fine sand – beach sand, 1+1/2 regular sand – bigger dimension of sand granules),
  • 1 cup of small rocks – aquarium rocks are recommended,
  • 1 coffee filter,1 rubber band,1 tablespoon,1 large spoon,cotton balls.

Now you can begin: pour the “dirty” water into that two liter bottle. Next step is “aeration” which will allow gases to escape and also will oxygen the water. Place a cap to the bottle and shake it for about 30 seconds. Pour the water in the bottle with the top removed that you prepared before and then pour it back in the “full” bottle, repeat the operation about 10 times. Next we’re looking after coagulation, that is the process that makes the solid particles hold on to each other (chemical process). Once coagulated these particles can easily be removed. We will add two tablespoons of ALUM to the aerated water then stir slowly for about 5 minutes. Now the particles will tend to stick one to another, forming bigger particles which will have less chances of getting through the filter. Once they got bigger the particles will “fall” to the bottom of the recipient, process called sedimentation. The water will change it’s color and will become more clear.

Start building the filter using the bottle with the bottom removed. On the upper side of the bottle attach the coffee filter (over the bottle) and to make sure it won’t fall off use the rubber band. Turn the bottle upside-down and place it into a recipient capable of retaining at least 2 liter of water. Put the small rocks into the bottle, the big granules sand over the rocks and the fine sand on top of all that. This is the filter you are going to use, but first you need to “wash” the filter. Pour about 2 liters of clear water over the filter. You should pour that water from a small height so that you don’t disturb the top layer of sand. After the water gets into the recipient you must pour it away and make sure the recipient is empty before you start pouring the “dirty” water. Don’t pour all of your “dirty” water, use only the top ¾ of it.

The water you obtained should be very different from the one you began this experiment. The last step of the process would be chemical treatment of the water, which is dangerous and an only be made by experts. This kind of water filter can be built at home. It can be useful if you you remain trapped inside the house and you’re out of clean water, but you have some source of dirty water. For better results you can add some cotton balls to your filter. For best result you can use cartridges that are built just for that, filtering water. This way you can eliminate bacteria, chlorine and heavy metals, making your water better than the bottled water which some experts say that is not that safe as producers claim. You can find the cartridges on

Well, as we see, it is quite easy if we are at home, we have all the materials we need. What if we are lost in the wilderness? Water is the first thing we are going to look after, before sleep and food. Too make a water filter in the wilderness you need several objects, you can try to find them or make them. The water might not be as clean as the one you obtain at home, but its good enough to keep you alive.
First you need a recipient. Whatever “metal can” you can find or something like that. Put some holes to it’s bottom. If you can’t find the recipient you have to make it out of something. For example take a large leaf and make a cone out of it. Make sure at the end of the cone there is still a small hole. Place some small rocks as the first material at the bottom of the recipient/cone. Over it you can put some gravel or sand, what you can find in the area. Try to find a big recipient, the more layers it can take the cleaner the water will be. If you can’t find small rocks you must place some grass over the rocks so the sand doesn’t get out through the rocks layer. If you cant build a filter large enough to clear your water you can pour it more than once through the filter.The best things you can hope to find are a metal cone and a metal can, as you see in the pictures.

Then you must take care of the bacteria in your water, that the filter doesn’t remove. The most common way to kill the bacteria is boiling the water. Then you have the unwanted chemicals that you have to remove. That’s the hardest part and usually close to impossible to obtain in the wilderness. You need other chemicals in order to neutralize those that the water contains. No matter how unsuccessful you water filter will be, at least you will survive (in real situations if you drink this kind of water you might get ill, but you will stay alive for at least few more days, longer than if you don’t drink water at all).

A note on reverse osmosis

Without going into chemical details, we will just note reverse osmosis as a filtration process used mainly for water. It is considered to be the safest water purification process. Yet, there are some hidden dangers to the reverse osmosis process.

First, in an attempt to leech out pollutants from the water, naturally occurring essential minerals are often leeched out as well. This is an unavoidable phenomenon, causing water to become too pure. In the absence of these minerals, which are chemically basic, water attains a slightly acidic nature (pH below 7). This causes the body to charitably offer minerals from its bones, weakening them over a long term. Further, consuming such water over a long term can cause diseases as deadly as cancer.

Further, substances which are smaller than water molecules themselves, as many herbicides are, are not removed. This means that reverse osmosis should not be used as the only purification method.

Not to mention the amount of water the process wastes! Performing reverse osmosis on a large scale is not the greenest way to purify water. Start drinking smart, and use methods other than reverse osmosis to purify your water. Combining it with UltraViolet radiation or distillation is recommended.