Cheap and Easy Gravity Water Filter





Introduction: Cheap and Easy Gravity Water Filter

About: Minimalist backpacker.

When I’m off hunting and fishing at the camp, I usually bring clean water. But I like to have backup option. The thing is that « real » and safe filters are way too expensive to use merely as backups. That’s why I like to use chlorine dioxide (by Pristine), that give a better taste than Iodine. Also, the steripen (the Classic model) offers quick, easy and very safe way to treat water. But I was a little disapointed with its prefilter, that is 40 microns wide.

Here’s a quick way to transform an emergency straw type filter into a gravity flow drip system that can filter nasties down to 3 microns. Exit the tubing, valve, collapsible water container, glue, CamelBak, and ... technology.
Keep it simple and light!

Step 1: What You Need

one 2 liters soda bottle (5¢!);
A Pristine Pioneer Emergency filter or Aquamira Frontier Filter. May not be the safest filters out there, but remember; I use this setup as a prefilter and a backup, before treating the water with UV or chemicals. You can buy one for about 15$. It can filter about 75 liters (enough for a fishing season!)
That’s it.

Step 2: The Funnel

Ditch the cap. Using a knife, cut open the bottom of the (empty) bottle to make a funnel.

Step 3: The Filter

Ditch the straw. Insert the filter tightly in the bottleneck, making sure the output end of the filter is on the outside of the bottle. With the bottle I used, the seal was quite tight. I guess one could use a length of tape to make it really watertight.

Step 4: The Drink

Fill the funnel with water, and put it over your bottle. It drips slowly, but take a deep breath...

Now you’re ready to drink, or to treat your water more thorougly with chemicals or UV. If the water is very dirty, you can cover the input end of the filter with a coffee filter and a rubber band, in which case the flow rate will probably be reduce.

If you don't want the filter to stand deep in the bottle (like on the picture above), you could make a stand out of a smaller soda bottle. Cut the bottom and the neck to make a tube, and put it between the Nalgen and the funnel.

Also, one could attach some wire on the funnel, so you can suspend the filter above your container.



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    13 Discussions

    IDK how good it actually works but I've seen people fill about 30 ft of garden hose with sand and pulverized charcoal ( from a fire not a bag) and fit the end into a pvc bucket on a pulley. fill the bucket with water and its pretty clean after pushing down through all that.

    I wouldn't know how to test the level of filtration but it was interesting.

    1 reply

    this ^^ was the instructable I was expecting to read about here, not "cheap and easy water filter - all you need is a bottle and a water filter". great idea!

    has anyone tried to make a ceramic filter from the clay that would be available locally (i.e. stuff that you would dig out of your back yard and fire). just a thought, if you were to form a piece so it would fit into a piece of PVC snugly use food grade silicon calk at the top and bottom. Leaving a space at the top for a water reservoir........

    it isn't hard to filter our solids the problem with "nuclear contamination" is that it can be far smaller than 2 microns as with some of the release from japan. second the water itself can become radioactive when exposed to a strong source, like the core of a reactor, so no amount of filtering can help there. thankfully water has a short half life (a week or two and it should be safe enough) I personally haven't done any tests but if you're that concerned get a gigercounter and learn how to use that to check the before and after product to be certain it's within safe limits.

    well almost never as radioactive hydrogen isotopes are extremely rare and there are no radioactive isotopes of oxygen

    actually there are 14 known radioactive isotopes of oxygen. check the "chart of nuclides" which contains all known isotopes of all known elements. anything can become radioactive from water to air to dirt. if it is exposed to a neutron source with proper energy (like uranium fissioning) granted a large number of half lives aren't very long pure water drawn from a working reactor is by itself radioactive for a while. i will agree with you that on their own radioisotopes of hydrogen and oxygen are extremely(!!!) rare the above post was not as i believe directed at getting the 1 in 100 billion chance that a stray molecule is present but to the larger concentrations found after a nuclear disaster be it a reactor issue or some nuclear weapon. this case anything that was in contact with the reaction directly will be to some extent "hot".

    Water is never radioactive its the uranium or plutonium that is radioactive in the water. What I mean is that radioactivity does not "rub off" on other substances because ionizing radiation is only emitted from radioactive atoms (Uranium, Plutonium, Carbon-14, ect...) only water with a radioactive isotope of hydrogen or oxygen could its self be radioactive

    for a filter that will work for your needs, look here
    I have one of these (for hurricane season) and they work great, but use a good prefilter, to remove larger particles from the water, or you'll be cleaning it every 3 days.

    I like it but I am afraid this only works with non-turbid water, right?

    1 reply

    I can vouch for the bandana method. You could put that over the top of the 2 liter opening to get the floties and some of the mud out. The coffee filter could be a stage 2 and the straw filter part 3.

    We did it with some stream water when we filled up a pump style filter. We bandana screened the particulate out then the pump would do 3 microns. We chemed it after pumping just to comply with the camping regulations but it probably wasn't necessary.

    Brilliant! Nice KISS pre-filter.

    RE: Turbid water: He recommended using a paper coffee filter. You could also stuff a bandana, strip of cotton cloth, or whatever in the funnel to reduce the solids before it gets to the filter.