Freshwater is a scarce resource; only 1% of the earth’s water is reachable by humans. Then an even smaller percentage is actually pure and directly drinkable. The rest may have varying degrees of contaminants like sediments, bacteria, minerals, etc.
Building your own water filter can be a fun task as a science project, yet it can also save your life if you’re stranded in the wilderness with no freshwater.
Although this filter cleans most of the turbidity and sediments, the water may still need further steps to be drinkable.
In this article, we’ll walk you through all of the steps you need from start to finish, so let’s begin!
Design #1: Bottle and Cup
In this design, you’ll create the simplest form of filters. It’s great for emergency situations, as well as science projects for young students.
- A plastic bottle. This is where the filter materials will be put, so pick the size accordingly.
- A cup, or another clean container to receive the filtered water.
- Clean cotton or coffee filter.
- Fine and coarse sand.
- Gravel or pebbles. You can purchase both sand and gravel at your local Home Depot store, or any other home/construction store.
- Activated carbon/charcoal. You can find it at your local pet store.
Step 1: Cutting the Bottle
Cut the end of the bottle that’s opposite to the cap with a scissor or a knife. Through this opening, you’ll put the filter materials during the DIY process and the contaminated water after you finish. Therefore, make sure the cut area doesn’t have sharp edges that can hurt you later on.
If you’re a kid doing this as a science project, it’s better to do this step under adult supervision.
Step 2: Opening Drain Holes
Open multiple holes in the bottle’s cap with a scissor. This is from where the clean water will get out of the bottle.
Similarly, kids shouldn’t proceed with this step unless under adult supervision.
Step 3: The Membrane
Put the clean cotton or coffee filter right over the cap.
This layer acts as a permeable membrane. It prevents layers above it from going through the drain holes while, simultaneously, permitting the water to pass. You can use any cloth or fabric if the suggested materials are not available.
In case you’re in the wilderness, using grass will do the same job and additionally give the water a natural taste due to the chlorophyll.
Step 4: The Carbon Layer
Put a one-inch layer of the activated carbon. Increase this thickness to three inches if you’re using a large bottle. In case you purchased the carbon in chunks, use a hammer to break it into the smallest pieces possible. The smaller you can go, the more surface area there’s to filter the water.
This layer is the heart of the filter. The activated carbon removes most of the dissolved organic compounds and sediments, which drastically enhances the water’s color, odor, and taste. That’s why you can find it in nearly all commercial filters.
Step 5: The Fine Sand
Put a 2-3 inch layer of the finest sand you can find. Usually, this sand is mixed with salts and chemicals, which will make the water undrinkable. So make sure you ask the seller about the sand’s constituents before purchasing.
This layer, and the following ones, act as physical barriers that filter out particulates from water. As you’ll see, the layers will increase gradually in particle size, so as to filter the bigger sediments first and leave the finest to the end.
Step 6: The Coarse Sand
Add a 2-3 inch layer of the coarse sand.
Step 7: The Gravel
Add a 2-inch layer of gravel or pebbles.
In addition to the filtration of coarse objects, this layer allows you to pour the water inside the filter without displacing the sand. This is especially useful if you’re in the wilderness trying to fill water from a running stream or waterfall.
Step 8: Pouring and Collecting
Put the bottle inside the cup or any container of your choice. Make sure the bottle’s cap doesn’t touch the bottom of the cup, so the filtered water can flow easily.
Pour the contaminated water through the cut part of the bottle. Do this as slowly as possible; this will ensure that every layer will stay in its place.
Wait for the water to go through all the layers and, eventually, collect in the cup. If the water is still cloudy, give it a second cycle of filtration.
Bonus Tip: Optional Layer
Add a membrane layer between each of the filter layers. This will prevent the materials from mixing together, which will increase the filter’s efficacy and lifespan.
Design #2: Two Containers
This design uses the same principle as the first one, but with a better design that gives a higher volume of pure water. This should be your design of choice if you’re planning to use this filter for a long period of time.
If any step is not clear enough, watch this detailed-process video to understand.
- Plastic bottle
- Fine and coarse sand
- Small pebbles
- Activated carbon
- Two bucket-sized containers with lids
- Plastic water faucet. You can find it online or at your local plumbing store.
Step 1: Opening Holes in the Bottle
Open multiple large holes in the bottle’s bottom. It’s better to use a professional tool like a driller. Regular home tools, like scissors, may disrupt the bottle’s integrity.
Additionally, open small holes in the bottle’s cap, just like design #1.
Step 2: Cotton Layer
Put cotton inside the bottle from the cap’s side. Condense it to the bottom with a stick until it reaches 2-3 inches in thickness.
Step 3: Layering the Filter Material
Like we established in design #1; put the carbon, the fine sand, and the coarse sand respectively in the bottle through the cap’s side. Use a funnel to make this step easier. Each layer must be 2-3 inches in thickness.
Add 2-3 inches of pebbles only if you can find pebbles that can fit through the bottleneck.
Finally, cover the top with a 1-inch layer of cotton.
Step 4: Preparing the 1st Container
Drill a hole in the center of the 1st container’s bottom. The size of the hole has to match the size of the bottle’s top.
Step 5: Attach the Bottle to the 1st Container
Use glue or a wax gun to attach the bottle to the hole you made in the 1st container.
Step 6: Preparing the 2nd Container
Drill a hole in the center of the 2nd container’s lid. The size of the hole has to be slightly wider than the size of the bottle’s bottom.
Drill another hole in the bottom side of the 2nd container. The hole’s size has to match the faucet’s size. Then attach the faucet to the hole with a wax gun to prevent water leakage.
Step 7: Putting It Together
Put the two containers above each other, so that the bottle attached to the 1st container passes in the hole you made in the 2nd container’s lid.
Step 8: Pouring and Collecting
Pour the water in the 1st container. The water will go to the bottle through the bottle’s cap.
Then after crossing the filter layers, the water will drain through the holes in the bottle’s bottom and finally collect in the 2nd container.
When you need water, open the faucet and voilà!
Sterilizing the Filtered Water
Whatever design you choose, the water may still hold biological contaminants, like bacteria and viruses, which can’t be filtered by the normal physical means. So, an additional sterilization step is required.
Sterilization by Boiling
According to WHO, boiling water for at least 1 minute kills most of the pathogenic microbiological organisms.
This 1 minute is timed after the water starts to boil, not after you put it on the heat source. If you live in an altitude higher than 5000ft/1000m, boil the water for at least 3 minutes. Then, let the water cool naturally.
If you find the water’s taste strange after boiling, don’t worry. This happens because some dissolved gases and volatile compounds are lost during boiling. Adding a pinch of salt to every liter can restore the normal taste.
Sterilization by Sunlight (SODIS)
Sunlight is one of the oldest methods used to clean water. This is because the ultraviolet rays carried in the sunlight tear up most of the microbes found in water.
Fill a transparent non-tinted bottle with water and leave it in direct sunlight for 6 hours. In cases of a cloudy atmosphere, leave the water for two days consecutively.
Disinfecting by Chemicals
Chlorine is a potent disinfectant that can be safely ingested in certain concentrations.
Use fresh liquid unscented chlorine that has “suitable for disinfection” on its label. With a clean dropper, add 8 drops of the 6% solution or 6 drops of the 8.25% solution per gallon of water. Stir and let the water stand for 30 minutes.
Whether you’re doing it for fun or function, this hand-made water filter will remove most of the water’s turbidity and contaminants by the physical means of carbon, sand, and gravel.
However, it should only be used if there’s an emergency that hinders the accessibility of pure water. Because even after the sterilization methods we mentioned, you can’t be fully sure the water is clean.