Water Filter Design


Problem Statement:
1.8 Billion people around the world do not have access to safe drinking water. Millions of people in both developing and developed countries are stuck in a cycle of extreme poverty. They lack access to clean drinking water and adequate sewage disposal. Major businesses do not want to get involved in providing clean water to these areas because they can not afford to design radically affordable products, which are needed and desirable for people who live on less than three dollars a day.

Objective: To design and construct a working Biosand filter that could provide clean drinking water to people of developing countries.

Specific Area of Interest:
Our Target area is Tonle Sap, a rural fishing village in Cambodia.


We are interested in designing affordable biosand filters – both small (personal use) and large (village / small community). We plan to design and build filters based on the research conducted by last quarters class on Water for Cambodia and our own research. The goal is to create a low cost design that allows many (if not all) materials to be sourced locally.



  • Use existing biosand filter design. Maybe rethink the vessel that holds the sand, etc?
  • 55 gallon drum with a bladder: drums are inexpensive and available worldwide (can use old, cheaper ones). Bladder with pvc pipe fittings would be easy to ship and rest of materials sourced locally. Allows the filter to be sanitary.
  • idea of what bladder could look like (smaller version w/ valve would be optimal – allow pvc pipe to be connected)
  • 55 gallon drum

Decision Matrices:
Google Doc of Matrices

Research questions:

  • How do you properly construct a Bio Sand Filter (with inexpensive materials from your local hardware store)?
    • PVC piping, 5 gallon buckets, and silicon glue can all be found for a relatively low cost at home depot.
  • What is the ratio of fine sand / coarse sand / pea gravel / larger stones?
    • The jury is still out on this one, but the consensus of the available literature is that the important ratio is sediment grain size to sediment layer thickness, and ratios between the layers of different sediments is less important.
  • What is Schmutzdecke?
    • Schmutzdecke is a dirty layer consisting of decomposing organic matter, Iron, manganese and silica. It acts as a fine filter that contributes to the removal of fine colloidal particles in the raw water. It doubles up as an initial zone of biological activity, providing some degradation of soluble organics in the raw water, which is useful for reducing tastes, odors, and color.
    • For more information click: schmutzdecke
  • What is the best way to promote early stage growth of schmutzdecke?
    • The ripening time for schmutzdecke is typically 2-3 weeks, but reaches optimal productivity after 7 weeks. Schmutzdecke develops best in warmer temperatures and when raw water is used due to its higher biological productivity.
  • Will we need pre-filtration (wire mesh / cheesecloth) to protect the bacteria layer (schmutzdecke)?
    • We found that a simple diffusion plate would suffice to protect the surface layer of shmutzdecke and would also preserve the composition of the sand layer
  • Will we need a screen (fabric or mesh) in between layers to keep the ratios intact & pipes clear or sand?
  • What areas are more suitable for a bio-sand filter?
  • What can & can’t be filtered out?
    • According to the EPA, slow sand filters do not completely remove organic chemicals, dissolved inorganic substances unless a granular activated carbon layer is installed.
  • What does our end user need to be filtered out?
  • How can we utilize biochar?
    • Biochar, (biologically activated charcoal) could be added to the filtration matrix to further remove contaminants from the water. The problem with adding carbon directly into the sand or gravel is that it is only effective for a number of weeks and there would be no easy way to remove the used carbon. One way to get around this while still using biochar would be to construct a smaller, secondary, filtration unit that can be easily attached and detached to the spigot of the filter for some last minute purification.

Helpful Links:
Diffuser Plate
Basic Knowledge
Detailed Design Template (Drum)
CAWST Manual
Study on smaller filters

Tracking our Progress:

Date What we did Picture
1/25/16 Try to create a biosand filter with two buckets (small one for the top part, big bucket for the bottom part) and pvc pipes IMG_7734.JPG
  • The first prototype pictured with samples of filtered / non-filtered creek water.
IMG_4260 (2).JPG
2/9/16 In our research, we could not find information for effective bio-sand filters for the one-bucket filter we made. (Bio-sand filters require a certain depth of filter sand to be effective.) So, using the research and specific instructions to make an effective filter, we made a new filter — this time 3 buckets tall. IMG_7813.JPG
2/21/16 Inside photo of 1-bucket filter. From bottom to top- Rocks, gravel, sand in place with a sand & silicone lining to mitigate sand slipping down the sides of the bucket to the bottom. IMG_7753.JPG
2/29/26 Brought the 3-bucket model to the SEF & cleaned the fine sand,
Second prototype while filling it with gravel and sand.

As a result of our attempt to build a bio-sand filter we created two prototypes that operate with varying degrees of success. The first prototype, the single bucket model, was a good stepping stone, but ultimately contained too coarse-grained sand and not enough filtration medium to adequately purify water to consumption quality. We kept the first filter full with dirty creek water for the majority of the quarter to grow the bio-film layer (Schmudztecke) in hopes that it would increase the purifying power of the filter. Despite our efforts the schmudztecke never grew, but the first prototype was still useful as an introduction/warm up to bio-sand filters. Our second prototype employed the use of three 5-gallon buckets stacked vertically to allow for triple the filtration of the first prototype. Finer grained sand was used for the filtration medium of the second prototype, but sadly we were never able to test out the second prototype due to a structural failure while installing the filtration media at the SEF.

What we learned from our efforts is that perhaps the bio-sand filter is not the optimal solution for the developing world. . There are far better options available on the market (lifestraw, Uv-pen filters) and in development ( Airdrop irrigation, UV chambers) that make the biosandd filters largely irrelevant. The 3 biggest problems with the Biosand design are 1) Big and Heavy 2) inadequate and unreliable filtration and 3) expensive to source.
The large amount of sand needed to filter the water and the fact that the filter needs to remain full of water to maintain the schmudztecke makes it very heavy. The filtration by the sand and schmudztecke neutralizes biological threats, but does not remove heavy metals from the water supply. Furthermore it cannot be quickly constructed and once constructed it is not functional until the schmudztecke develops, this makes it very impractical and unreliable as small disruptions in the biological community can render the filter useless. Lastly acquiring sand of fine enough grain size is not practical in the united states, let alone the developing world. Unless the area was next to a dried lake bed, it would be very hard to locally source the correct sand. Ultimately, we scrapped the prototypes as we figured the materials would be better put to use to a new project than continuing to fumble around with biosand filtration. In the future we would suggest to groups that are interested in providing clean water to the developing world to explore other options.

Contact Info:
Group email: calpolybiosand@gmail.com
Daniel, Cody, Mariah, Julia, Jordan

IMG_4196 (1).JPG