The pond filter experiment

The pond filter has been running for about 7 months now. It has frozen solid twice, however it did thaw out both times and it is still working. The most recent test showed less than 2 coliform bacteria per 100 ml of filtered water taken from the output of the filter. The most recent occurrence at the pond was a swimming event enjoyed (I presume) by raccoons. The water was full of mud, and the pond looked like a mud puddle with the water mostly opaque brownish-green. This type of event happens regularly. The leaves and other decayed organic material had clogged the pump and the water was just barely circulating. The raccoon event resulted in the loss of the fish that were in the pond. After cleaning the little pump and testing the flow, the filter was running again. Within less than 24 hours the water in the pond was clear.Clean water from the filter

The sand has settled on the bottom and the rest of the nasty stuff in the water has been removed by the filter.

Now, why is this significant? Why am I even bothering with this? Well, this is actually an experiment to determine if it is possible to put together a working slow sand filter with very, very coarse sand (.45 mm effective size) and only a flat rock inside as a baffle. The answer is yes. Now, I would not recommend drinking this water, but it would be acceptable to use it to water a vegetable garden, or to do laundry with, or just about any use except drinking – but this filter is cleaning water that is extremely contaminated – far more than any source a person might use for drinking water such as roof water or water from a shallow well which would not contain mud, nor have critters wallowing around in it. So the next step will be trying a similar set up with water that is reasonably non turbid to start with and only moderately biologically contaminated, such as roof water. . . more later.

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9 Responses to The pond filter experiment

  1. Steve M. Grube says:

    Great blog and an exceptionally good website about slow sand filters –which got me thinking about building one of my own.

    I live on a remote patch of coastline in northeast Brazil, about 200 meters off the beach. I recently had a well put in, and the welldiggers only had to go down about 6 meters to hit water. They warned me ahead of time that this water, while perfectly alright for cooking, cleaning, showering and watering plants, would have a faint salty taste to it and slight odor. And it does. Not horrible to drink, but nothing like a cool, clear delicious glass of fresh well water from, say, two hundred feet down in the middle of Illinois (my home state).

    So here is my question: is a sand filter capable of removing this salty flavor and slight odor of the water six meters beneath my property or would I be wasting my time in building one? I´m not eager to invest in a solar still. Harvesting rain water is certainly an option, as the rainy season brings near daily showers. But I want to take advantage of the well I already have.

    Many thanks!

    Steve Grube

  2. admin says:

    Interesting. I know slow sand filters remove hydrocarbons but I am not sure about salts, or odors, If the odor is not strong a SSF might take it out. I don’t know for sure. I guess it depends on what is causing the “salty taste” and what is causing the “odor”. You probably would not be wasting your time, because you will need the slow sand filter for the rain water harvesting anyway if it does not work to improve your well water. Also, you could use the well water for everything except drinking, and the harvested rain water for drinking, after it runs through the filter.

  3. Steve M. Grube says:

    Many thanks your speedy and honest reply.

    Yes, my thoughts are pretty much the same: since a sand filter is relatively cheap and easy to build (and mainly because I love to fart around with self-sufficiency projects like this) I´ll just go ahead and build one and see what happens. All the materials are readily available around here –and there sure is no lack of sand. Basically, I live on top of one huge sand filter!

    The current roof on my house will not do for collecting rainwater, which, as I said earlier, falls in copious amounts during the rainy season. It´s made from coconut tree leaves and there are no gutters.

    Let´s imagine that I wanted to process, say, six liters of drinking water per day (I live alone) using rainwater and a 55 gallon drum-type SSF. If I were to construct some type of rainwater capture system, say a large plastic tarp –or even some heavy canvas cloth– suspended from four poles, can you give me some idea how large this tarp would have to be to ensure a six-liter-per-day output?

    Also, the average temperature here (6 degrees south of the equator) is obviously very warm. Can you give me some ballpark idea how long it would take for the schmutzdecke to get up and running?

    Thanks again!


  4. Steve M. Grube says:

    You know, I got to thinking about this question of tarp size, and I decided it was kind of a stupid question. With some of the heavy rains that we get down here, I imagine that a handkerchief-sized tarp would be more than sufficient. Hell, during SOME of these rains, I could just stick a five-gallon bucket out in the yard and it would get about half full.

    Anyway, I would still appreciate any observations you might care to make on the subject.


  5. admin says:

    Did you mean 6 liters per hour? I think you can easily process 6 liters of water a day. Filter 1 which is the slowest filter in the test, has a flow rate of 11.15 liters per hour and I have not cleaned it for over 2 years – its still producing excellent water. The other two larger filters are at about 25 liters per hour, and the experimental pond filter is at 50 or 60 liters per hour.

    The biofilm will probably take about 3 weeks to form depending on how much life there is in your water. However, I would highly recommend testing the water carefully before you ever consume any. And furthermore, i would have the water tested regularly, or alternatively just use a uv filter at the point of use. Small UV filters will easily run on a small solar panel, and a small deep cycle battery. If you are where there is lots of sunshine, you may not even need the battery! I have learned that water can vary drastically as far as biological contamination. Sometimes several cfu’s per 100 ml and then for no apparent reason 30,000 cfu’s per 100ml.

  6. Steve M. Grube says:

    Again , many thanks for your prompt and informed reply.

    You know this whole discussion is kind of getting me revved up to make some serious amounts of good drinking water and give it to my neighbors around here.

    Yes, actually I was talking six liters per day and not per hour –and I doubt I´d even be able to drink all that. When I read that your SLOWEST filter has a flow rate of over 11 liters per HOUR and that you haven´t had to even touch it for two years, I get to thinking about other possibilities, taking this to a much larger scale.

    It´s not that my neighbors are in dire need of drinking water; it´s readily available in stores, sold in plastic 20-liter bottles at about $4.00 each. Not a big deal for just one person, but when there are families of up to 12 persons to keep hydrated, the economics of drinking water get very serious indeed.

    As is happening all over the world, food prices are skyrocketing in Brazil, and the price of water is moving right along with it.

    Brazil, of course, is blessed with abundant fresh water (approximately 13% of all fresh water on the globe is here) , but Brazil has a miserable transportation / logistics system and water prices reflect this.

    There is one deep well where I live (a placed called Lucena, just north of Joao Pessoa in the state of Paraiba), and the water is excellent, truly delicious. But the owner is old, cranky, unreliable and one never knows when he´s going to make his delivery rounds –which he does by donkey cart, by the way. And I haven´t had the courage to ask him if his well water has been tested recently –or ever, for that matter. He, of course is completely illiterate.

    Yes, there are several good universities within an hour drive of here that provide free water testing, and I will definitely have the water tested before I drink one drop of it.

    All of this to say that the plot is thickening. I think the minimal cost and effort involved in building a good SSF would make the whole project rewarding and interesting. I´d start small. An SSF putting out 11 liters an hour would be ideal to provide two or three families with drinking water. And if people saw me doing this, I´m sure some of them would want to build their very own SSF.

    Let me do a little more thinking on this. I want to talk to some local families and see what their interest is.

    I´ll get back to you with other questions, and thanks again for your help.

    Please free to send along any other information, ideas, cautions or encouragement as they come to mind.

    Also, feel free to send stuff to my email address:

    Tchau, tchau


  7. Jason Perez says:

    Hello. Thanks for the great description on building a first-flush diverter out of 55-gallon drums. I am now just getting started with rainwater collection. Gutters are installed and I have two large tanks (1000 gallons and 1550 gallons). Just need to move the tanks into place and construct the piping from the gutters to the tanks. I had already purchase a first flush filter ( but the volume stored isn’t enough. And the 55-gallon drums are a lot cheaper so I’m going to hit the hardware store this weekend to get all the parts (already bought two 55-gallon drums, same as in your pictures).

    I’m going to use a 4″ outlet to the tank to provide for maximum water flow. Don’t have a ping pong ball so I’ll have to get one of those too!

    It looks like you have a small sink type drain in the inlet pipe, correct?

    I’ll already have leaf filters on the downspouts so I won’t use the course screen in the flush piping, and I’m going to connect the 4″ pipe directly into flush filter (tank opening is 68″ high).

    What size hole did you drill into the drum? 2-inch?


  8. wes parker says:

    I like the idea of recycling water and using it for needed projects around the house. That should save water and be economical at the same time. I live in the Pacific Northwest and am interested in the concept. I do not have much knowledge in the area, but would will research some more. As a koi lover, i am also wondering how the water quality tests out with said filtration with the koi in the pond. Thanks for sharing!

  9. admin says:

    Wes, Jason, and Steve thank you for the comments.

    The input of the diverter does have a stainless steel strainer made for a sink drain. I have 2 screens one coarse and one fine, made from steel wire. The hole saw I used for the larger (2 inch) adapter was a 2 and 1/4 inch diameter hole saw. The hole can be (almost) easily drilled with a brace and bit style hand powered drill. The adapter will thread into the plastic barrel nicely. It does take some pressure to get it to thread, but it does work – be sure to use an o ring to help it seal. The vent is a must or the thing won’t work – and be sure the vent opening is higher than your output pipe or the water will just pour out the vent instead of the output. I was skeptical of the ping pong ball’s longevity but, as of now, (2011-02-26) the ping pong ball is still working. I think its a good idea to have a large output to the storage, particularly if one is in an area that gets heavy rain for a short time and then no rain for months on end – one does not want to lose one drop of water in that case.

    As far as the pond, It will be a while until I can test the water again with fish in the pond, as something, (raccoons) got the fish and the weather has been below freezing here for a week now so the pond is inactive. After 4 winters of testing slow sand filters, I have found them to work at near freezing temperatures, and after being frozen solid for as long as 10 days, they rebound within a few days and continue to function. Also, the filters that handle shallow well water have not frozen as quickly because (I think) of several things: 1. the water 10 feet below the surface is a lot warmer than at the surface and most certainly not freezing in this part of the world (north west Washington state) and, 2. I have a 50 watt light bulb right over the pump motor to keep it warm. 3. The pipe from the well is buried deep. 3 and the water is kept running 24 hours a day. I might add that all the pumps I have here can be easily powered by one pv array with 1 deep cycle battery – still not perfectly sustainable but much better than using chlorine, and massive amounts of fresh water to backwash a rapid sand filter and then huge amounts of petrol to haul away the mess and then . . . . oh well, you get the picture.

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