How To Make your Own
Gravity Water Filter
       How To Build A Bio Water Filter

Written by: Rich M How-ToAugust 12,

Everyone who talks about survival eventually talks about water filtration. You see all kinds of reviews on this
water filter and that—whichever is the favorite of the person doing the writing. Yet, almost all of them have
one failing in common; the filter element eventually has to be replaced. While there are a few filters on the
market that are backflushable to clean them out, there are only a few.

Of course, if there’s a general breakdown in society, for whatever reason, availability to filters or filter
cartridges will be essentially cut off. That means that whenever your filter supply runs out, you’re going to be
left with a huge problem. Since the water probably won’t be safe to drink, you’ll have to boil or distill enough
for your needs, a slow process.

The biggest risk in drinking most water is that of waterborne pathogens. Bacteria, protozoa, and other
microscopic parasites can be found in almost any water supply, some of which can kill you, and many of
which can make you wish you were dead.

The other problem that you might end up facing is chemicals in the water. Basically, filtering systems ignore
this problem, concentrating on dealing with the much more common problem of those pathogens. About the
only effective ways of dealing with chemicals is by neutralizing them or by distillation. Even with distillation, it
is possible to end up with some chemicals in the water, if the chemicals’ vapor point is lower than that of

Bio-filters, a Great Alternative

Another option, instead of buying expensive commercial filters and stockpiling them, is to build a bio-filter.
This simple filtering system is used worldwide to purify water for drinking. While it may not get out every
pathogen in the water, it will get out enough that you can safely drink the water, allowing your body to
destroy the few that manage to get through the filter.

Actually, a bio-filter works almost the same way that a sewage treatment plant does. The standard for water
treatment plants is that the water that leaves it must be clean enough to drink. To accomplish that, they use
a multi-stage approach to removing anything harmful from the water. Likewise, a bio-filter uses a multi-stage
approach to removing impurities and pathogens from the water, so that the water that remains is drinkable.
The only difference is that you can make it yourself.

Bio-filters have three separate layers:
•Activated charcoal

Each of these layers removes different things, leaving the water that comes out of them clean enough to
drink safely, even if you got that water from an ugly looking pond near your home.

The first layer, gravel, is there to remove large pieces of debris from the water. This would include things like
small sticks, leaves, the odd tadpole and bugs. The water then moves on to the sand layer, which removes
smaller particulate matter that managed to pass through the gravel. Finally, the water passes through a
layer of activated charcoal to remove bacteria and some chemicals.

Ultra Efficient Water Filter Fits In Your Pocket!

It is the activated charcoal that is the secret to a bio-filter’s success. Activated charcoal or activated carbon
(the same thing) is “activated” by blowing air through it. That air causes thousands of pores to open up on
the surface of the charcoal, making convenient places for absorption of chemicals via bonding and capture
of bacteria. The microporosity of activated carbon means that just one gram of it has over 500 m2 of surface
area. That huge surface area is what makes it so effective.

Building the Bio-Filter

To build a bio-filter, all you need are the three ingredients mentioned above, along with some food grade
five gallon buckets. You’ll also need some screen, a few plastic plumbing fittings and a hole saw.

There are several ways of going about this, but the way I like to do it is by using plumbing fittings between
the stages of the filter. By using a fitting, you can have better control over the water flow and help make sure
that the materials don’t migrate from one bucket to the next.

To assemble your fittings and build your filter, do the following:
•The fitting that is going to go on the inside of the bucket needs to have fiberglass screen stretched over it.
That can be held in place with a rubber band or O-ring. However, gluing it makes it more secure.
•Cut a hole in the bottom center of two buckets, which is the right diameter for the threaded part of the fitting
to go through. Cut the same size hole in the side of the third bucket, which is just above the bottom.
•Attach the fittings together, with the bottom or side of the bucket between them. The screened side of the
fittings should be up. Use an O-ring between the fittings to create a seal.
•For the bottom bucket, the one that has the fitting through the side, you may want to add a valve, an angled
fitting or a fitting with a flexible tube for the outlet. Whichever you choose should allow you to have the
filtered water go into a fourth bucket, pitcher or other container.
•Cut a hole in the center of the lids for two of the buckets, which is slightly larger than the fitting. You don’t
need a tight fit here, rather one that will make it easy to stack your buckets.
•To protect the screen from the weight of the sand and gravel, put a cover over it. The easiest way to make
this cover is with some small plastic cups. Drill a number of holes in the sides of the cups, so that the water
can get through. Then glue the cup upside-down over the fitting.
•Before putting your gravel, sand and activated charcoal in the filter, it needs to be rinsed thoroughly to
remove all dirt and silt. When you can put on these materials, without any dust fogging the water, then it is
rinsed thoroughly enough.
•You will need to fill each bucket 2/3 to 3/4 full of the filter materials. The activated charcoal goes in the
bottom bucket, which should be the one with the fitting on the side. Put one of the lids with the hole in it on
this bucket. Set the bucket for the sand on top of it, and the bucket for the gravel on top. The top bucket’s
lid does not need any hole in it. A plain lid can be used to keep any debris from falling into this bucket.

The finished filter will be able to process quite a few gallons of purified water per day. For the best possible
water, you’ll need to aerate it after filtration. Aeration is a simple process, which adds air to the water. You
can accomplish this by pouring the water back and forth a few times between a couple of buckets or pitchers.

Finished bio-filter, shown by a 750 liter (200 gallon) storage tank. The plastic tube on the front of the tank
shows the current water level as being about 1/3 full.