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Thread: gravity underground sand filter

  1. #1
    DIY Junior Member Bonnan's Avatar
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    Default gravity underground sand filter

    Looking for info to clean up cistern water before it is pump into my buildings.
    This is roof collected water not used for human consumption but must be reasonably sediment free. How does one design/build a sand filter for this purpose. Thanks for any help

  2. #2
    DIY Member gritres's Avatar
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    do you really get enough sediment off a roof to justify a sand filter? maybe just use a spin down filter

  3. #3
    DIYer, not in the trades LLigetfa's Avatar
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    How well a sand filter works by gravity would depend on how much head the water has. At some point I would think you'd need a pump to backwash the sand filter. Something like a swimming pool filter might work. Pond filters are another consideration.

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    Jack of all trades DonL's Avatar
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    Like LLigetfa was saying, You would need a way to backwash a sand filter.

    You may want to use something like a filter material used in pond filtration systems.
    You can buy it in large sheets, and cut to fit. Put in into a 5 gallon bucket with a IN/OUT connection and a locking lid.

    Then when the filter gets dirty, you take the material out and rinse it using a garden hose.

    I have built these before, but they are only for low pressure. High pressure will blow the lid off of the bucket when the filter get dirty.

    Should work good for gravity a system, and is cheap to build.


    DonL
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  5. #5
    General Engineering Contractor ballvalve's Avatar
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    dig a hole and line it with EPDM and fill it with sand. thats how septic tanks sand filters work. You could even backwash it - you would build a distribution grid of pipe with drilled holes in the bottom of it.

    Frankly, a big cow water tank would be easier to deal with. Need a lid though. grade sand at botttom to pea gravel to gravel at the top.

  6. #6
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by ballvalve View Post
    ...grade sand at botttom to pea gravel to gravel at the top.
    Would you not want to reverse the gradient, putting coarser on bottom and finer on top? That is how a septic leach bed is setup.

    I am considering sinking a couple of well rings at the end of where my underground pipes draining my rain gutters break to the surface. I'd just use a pond filter and a old pitcher hand pump to draw the water. I have solid clay so wouldn't even need to line it with EPDM.

  7. #7
    General Engineering Contractor ballvalve's Avatar
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    Yeah, you got me reversed, the gravel is to keep from washing the sand through the pipe holes. The size gradient is important.

    Or you could use a filter cloth.

    But actually a standard septic leach line with 4" perf is all 1.5" and a bit under.

  8. #8
    DIY Senior Member Smooky's Avatar
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    I found good information and diagrams for this type of slow sand filter in "Environmental Engineering And Sanitation" by Joseph A. Salvato, P.E. I have the third edition.

  9. #9
    Jack of all trades DonL's Avatar
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    Do you care to share Smooky ? Or are you just teasing ? LOL.


    DonL
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  10. #10
    Porky Cutter,MGWC Porky's Avatar
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    A simple small gravity feed plastic or metal tank will work. Feed the rain/roof water in the side of the tank and out from the top. Install a pipe plug (or ball valve) at the bottom and drain the sand out every six months to a year. This will work for all heavier than water debri trash.
    Porky Cutter, MGWC
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