How to Filter Water With Sand, Gravel and Charcoal 

Charcoal sand and gravel for the project

A “do it yourself” water filter using charcoal, sand and gravel is a cool project that everyone should try. It involves gathering some resources and putting it together to create a neat project. Here’s how I do it.

In order to create a water filter using charcoal, sand and gravel, fill up an empty water bottle with sand water and gravel. Pour in water through the top and collect that water in another cup. 

This experiment serves as a fun science experiment but it’s also a great way to learn more about a survival skill. If you are ever out in the wild and need water this method works perfectly. 

Required materials 

Here are all of the required materials you will need.

Dirty water from pond or lake

The whole idea is to clean up dirty water so you need the water to get this experiment going. If there is a lake or pond near your house, that would be a good place to start. Collect enough water so that you can do the experiment a few times in case you mess up or do something wrong.

2 empty plastic water bottles

One water bottle will be used for the filter and the other bottle will be used to catch the water. Alternatively you can use a large cup to catch the water. 


The cotton will sit at the base of the filter and prevent the other materials from falling through. If you don’t have cotton, check these cotton balls out (amazon link). I use it and they work great! 

Sand (enough to fill ¼ of a plastic bottle)

Sand is the 1st component of our filter as it’s one of the main ingredients of the filter. Here is the sand I use for my filter: (amazon link) 

Crushed Charcoal (enough to fill ¼ of a plastic bottle)

Charcoal is the second component of the filter. If you have charcoal you can grind them to get them to a sand like structure. If you don’t have charcoal you can use burnt wood or this charcoal that i use (amazon link). 

Gravel (enough to fill ¼ of a plastic bottle)

Gravel is the third component of our filter. You can collect gravel outside or purchase it from a store. Here is the gravel that I use: gravel (amazon link) 

Gravel is basically small stones so you can collect some small stones and use that instead. 

Paper towel 

Things will get messy so you want some paper towels or cloths to clean up any mess. A thick napkin or paper towel will do just fine. Here’s some high quality paper towel that will work well: paper towel (amazon link)

Filtering water using charcoal sand and gravel 

Ok follow these steps closely and don’t skip any part. This is all important and it’s necessary to follow carefully to do the experiment right.

1. Prepare your bottles 

You want to start with your two plastic bottles or your plastic bottle and cup. One will be used for the filter and the other will be used to collect water.

First, cut off the bottom or base of the plastic bottle. This is where we will insert all of our materials so we want the base as it is the wider opening. 

Take your second bottle and cut off the mouth of the bottle. It should be wide enough that the previous bottle can receive water from this bottle. This second bottle will be used to collect the water. You basically want to create a cup or a mug. 

Alternatively, you can use a regular mug or cup. But I usually have plastic bottles laying around so I go with that instead. 

Flip the filter bottle upside down so the mouth is sitting at the bottom. Place it inside the second bottle.

Tip: I like to use a sharper or marker to mark the area I’m going to cut. It makes it easier to cut the right part off. 

2. Add cotton 

You can use some cotton, fabric or some type of cloth. This material will serve as the base of your filtration system and hold up the charcoal. It will prevent the charcoal, sand and gravel from falling into the can. 

Take a few pieces of cotton and stuff it at the mouth of the water bottle. Make sure it covers most of the mouth. Also make sure that there is enough to withstand all of the incoming materials. I like to use 3 to 4 pieces of cotton.

Tip: The cotton will act to prevent materials from falling into our drip container but if you want to be extra cautious you can also cut some holes in bottle lid. It will secure the drip container but make the process slower. 

3. Next add your charcoal 

Slowly place the charcoal at the base of the filter. It should be sitting on the cotton. You should fill up the charcoal to get it to about ¼ of the bottle filled. 

4. Next add your sand 

Pour in the sand slowly. Sand can be a mess to clean up so you want to carefully pour it in. You should fill up the sand to get it to about ¼ of the bottle filled. 

5. Add in the gravel 

Slowly place the gravel inside the bottle. You should fill it up get it ¼ of the bottle filled. 

6. Pour the water 

Slowly start pouring in water into the bottle. You should not pour all at once as the water needs time to filter down through the bottle. 

7. Refill as necessary 

  • Refill the filtration system as necessary. You can tell when the bottle needs to be refilled when it is starting to look a little dry. 

8. Purify water 

  • The water isn’t safe to drink just yet. You still need to purify the water. There are several ways to do this. If you are doing this at home you can place the cup of water in the microwave for a  few minutes to make it safe to drink. 
  •  Since you won’t always have a microwave in the wild, you would likely use a campfire to achieve the same effect.  
  • If you really wanted to you could leave the water out in the sun but this would take a long time. It is essentially doing the same thing as the previous two methods but at a much slower pace.  

In the wild you can use burnt woods as charcoal. Obviously there won’t be an abundance of charcoal so pieces of wood that are burnt should be good. 

If you want to try more cool projects and experiments. I made this DIY cheat sheet with over 100 projects! Click here to check it out

Why filter water with charcoal, sand and gravel? 

This method will help you when you are in the outdoors whether you are camping or hiking and want some good water to drink but don’t have it around. Obviously we are not in the old times but it’s still a nice life skill to have in the event that you do get stranded somewhere. 

Another reason why you might want to do this is that it’s a fun science experiment! People love taking something dirty and turning it clean. It’s also great to do with kids. You can teach them a cool skill to have while keeping them entertained and busy. 

How does sand, gravel and charcoal filter water? 

The gravel layer catches larger particles. These particles can include anything from larvae or worms or other small bugs and critters. It can also catch leaves and twigs. 

The sand layer will continue to catch impurities. These impurities will be slightly smaller than those caught by gravel. The impurities include things like dirt and grit. 

Finally you have the charcoal. The charcoal will continue to filter impurities and also contain chemicals from passing by. 

As the water passes through the bottles different sized particles will be caught in the material. Some materials might get caught at the very top while other materials will be caught along the way. By the time it reaches the bottom of the bottle the water will have been cleaned thoroughly. 

Is the water safe to drink 

The water should be safe to drink as long as you followed the directions correctly. You really want to boil the water before drinking because this will kill off any of the particles that need to be killed. 

I would also compare the color of the water to regular tap water. You will notice that the water you started with is much more yellow than the water that has been filtered out. 

Does sand and gravel filter water? 

There are alternative ways to filter water and some of the include not using charcoal but only sand sand gravel. I haven’t tried this method out yet but I’ve heard that it can work if done properly. 

The secret to this method is doing multiple layers of sand and gravel. In our experiment we only used one layer of each of the components. Without the charcoal you need some extra protection and so that’s why you go with multiple layers of sand and gravel. 

To get this to you’d probably want to use like 3 layers of sand and 3 layers of gravel. You will probably want to experiment with how much sand and gravel to use but it should work. 

The rest of project will stay the same. 

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