Use vitamin C to de-chlorinate water

For those who use public water, chlorine can be a problem. It most certainly is a problem in a biological slow sand filter as it kills the beneficial bacteria that make the filter work. A possible solution is to add vitamin C to the water before it is used. This has been shown to work quite well.

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Will a DIY slow sand filter produce potable water?

We continue to get questions about the filters we describe producing “potable” water. Again, I’ll try to address this issue. These filters are not 100 percent foolproof and they are not magical. They require maintenance and specific actions to keep them able to purify water. Check the link to “potable”. There you will find a definition of “potable”.  Wikipedia also has a definition of “potable”: “Drinking water or potable water is water safe enough to be consumed by humans or used with low risk of immediate or long term harm.”

Know that the output of any of the slow sand filters we describe is totally dependent on operating conditions and proper maintenance. They are capable of significantly improving the quality of input water, however; there are no absolute 100 percent guarantees that any of these filters we describe will produce perfect water 100 percent of the time.

To determine if any of the small slow sand filters we describe might provide improved water quality, the filter would need to be set up and a pilot study done. This means the filter would need to be set up at the intended location where it will be running when in service, using input water from the same source all the time; and then be tested while operating in the worst of conditions and the best of conditions. This testing should be done by a qualified knowledgeable person. Also the input water would need to be tested to determine the extent of contamination. Then the owner / operator would need to be trained on how to properly use and maintain the filter. Even with all this, output may vary considerably and it is possible for any of the filters we describe to produce water that is not completely purified. Also contamination can come from anywhere; And anything can be in water – anything. Contamination can vary tremendously. A UV filter may be needed in some cases. If the condition of the input water changes and becomes more contaminated, or contaminated by different substances; then the output of the filter may also change, possibly becoming more contaminated.

Read all of the information we provide, and by all means, compare it with other studies;  and then make your own decision about how to use the filter you put together.

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Five gallon DIY slow sand filter update

The five gallon slow sand filter experiment, mentioned in September of last year (2013) is still in progress. Due to some unforeseen issues, the EPA tests cannot be done as of yet. We will attempt to start some field tests on the three filters (filter 10a, 10b, and 10c) as time permits.  These filters are still in the process of recovering from being totally frozen this winter. Until about early March, there was no water flowing through them.

A summary of what we have observed so far:
These filters will work, but there are some serious issues. 

It is necessary to keep the flow rate very, very slow; much like a dripping faucet. 

They are very easily disrupted if moved or bumped even slightly as the biofilm seal between the sand and the container may be broken easily – the sand and water in the bucket is so heavy it causes the bucket to flex if even moved slightly. As a result, the output is bad for about a week.  

They are inferior to the much larger 55 gallon filters we have running here, but most certainly better than nothing.

As an experiment, they appear to “work” to filter out some turbidity, and we have noted what appears to be some removal of biological contamination. The water that comes out of the roof water diverter and is poured into the top of these little filters is improved by running through them.

If anyone reading this has conflicting information, please post it here in the comments section below.

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Can I save money on my water bill by using a rain barrel?

If the cost of the water; and the cost of the infrastructure that brings the water to “you” and takes it away when you’re done with it are considered; then, on paper, a rain barrel will pay for itself in several months or less, providing the water that it collects is used on a regular basis. Most people don’t consider or even realize that their taxes and house payment are part of the cost of the infrastructure that brings water to them. When their land was “developed” for housing, the cost to put in water utilities was tremendous, and the upkeep is also tremendous. The developers pass all those costs along to homeowners; and county, city, and state taxes pay for these services. The true cost of water usage is a lot more than most people realize. When using rain water harvesting, the more water you use, the more you save. The opposite is true of public water usage. The more you use the more it costs.

The complete, accurate, true answer to this question is not a simple yes or no. If you’re talking  about “monthly cash flow”, and using a single 55 gallon barrel; your savings will be very little, or none at all, depending on your use. Know that this assumes that the cost of water, sewer, and / or “utilities” stays the same forever, which it does not; and that those infrastructural costs are not included in the “profitability” of a rain barrel. If only the cost of the actual water is considered, then it may take 3 or 4 years to pay for the barrel, depending on how often you use it. Financially, not a “high yield investment”.  The utility costs will go up as long as infrastructure exists. If it stops existing, then a rain barrel will be your only source of water, which will make it one of the most important things at your house. Also know that any amount of time over four days without water will be pure hell. A plastic rain barrel will last indefinitely, and you only pay for it once.

Now let’s look at an example:
Be aware that this is in an area where there is ample rainfall, and where it is possible to use the water from the barrel with only several weeks of freezing weather. This example will not hold true in areas of extreme extended periods of sub-freezing weather, or in areas of marginal rainfall. Also, contrary to popular belief, it is not against state government law to set up rain barrels in any state (except some places in Colorado). 

In the Seattle area, of Washington state, water (just the water; not the service) costs anywhere from  .667 cents per gallon  to 1.913 cents per gallon. (The lowest basic cost for water service is between 13.75 per month, to 16.70 per month regardless of use.) So 55 gallons of water will cost you anywhere from $.37, to $1.05 for the water only. This is not the “true” cost of the water; just the amount of “cash flow” you must pay for the actual commodity; which is water. Look at it as the instantaneous cost of the water. The $1.05 is summer cost, when most people are using water for gardening purposes. At the very least, a 60 dollar 55 gallon barrel would need to be filled and emptied 60 times to pay for itself, in actuality. For an average roof size of 1500 square feet, and a total of 4 downspouts with equal flow, with only 1 rain barrel on 1 of the downspouts, and;  allowing for 20 percent water loss due to evaporation, roof surface and leaks, 1 inch of rain will produce 186 gallons of water at 1 downspout. The Seattle area averages about 30 inches of rain per year. That’s 186 X 30 or 5580 gallons of water. That’s over 100 fills and drains of the barrel in a year. Paid for easily in 1 year – if it is used and if the rain falls at the right time. If it is not used, then it is not paid for. But there still is a problem with this. Rain does not always fall conveniently at the right times, so there may be times when the barrel will overflow, and that “overflow” water will not get stored to be used later. It may take 2 years, or longer to pay for the barrel. Keep in mind that this ignores all other costs of public water, this just takes into consideration the cost of the actual water. This also ignores the cost of cleaning up pollution that gets washed into lakes, streams, and oceans because of runoff that is not slowed down by rain barrels.


Note: (1500 X .0833 X 7.48 = 935 gallons / 4 = 233.75 gallons * .20 = 46.75  233.76 – 46.75= 187 gallons. )


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Designing a DIY slow sand filter: what to consider

I am writing this to summarize what has been learned here in the past 7 years of designing, building and operating small slow sand water filters – thousands of hours and hundreds of pages of documentation. The details can be found by searching this blog, or accessing each of the water filter websites  that are associated with this blog. This activity has had far more failures that successes. We’ve learned more from the failures.

The most important issues to consider when putting together a DIY small slow sand filter that will work to purify water follow:

1. Sand: Fine sand will provide better quality output at the expense of a very slow flow. Coarse sand will provide marginal quality output and a higher rate of flow than fine sand. A good compromise is to use .15 mm effective size sand and then provide storage for the output water. Never use “beach sand” from an ocean beach, there could be all kinds of contamination in it, including large amounts of salt and anything that can be tracked in by foot traffic. Know where the sand comes from to be sure there is no contamination. Mason’s sand, “play sand”, or commercial bagged sand is a good choice, but must be sifted first, and then washed until the water runs clear. The best, and the most expensive, is filter sand; processed specifically for water filtration and rated for potable water. The sand depth is critical. Very small diameter, shallow filters (4 to 5 inch diameter, and less than 12 inches deep) will not remove much contamination.

2. Container: We have used 55 gallon plastic barrels, 65 gallon plastic barrels, and 5 gallon plastic buckets. We also have one very small filter about 5 inches in diameter, and about 9 inches deep running here as an experiment. The diameter of a diy small slow sand filter is critical. As diameter decreases, flow rate must also decrease. See number 3 below for more on flow rate. Always be sure to rough up the inside of the container with sand paper. Make the lines of abrasion horizontal or random but NOT vertical. A smooth surface inside the container will allow un-purified water to slip down between the sand and the container surface. The 5 gallon filters we have tested here work marginally, but they do take out significant amounts of particulate matter. The biological tests done here on these small filters are field tests only; and are inconclusive at worst, and show some bacterial removal at best. The 55 gallon containers, and the 65 gallon containers work very well and the output of these filters has been tested by EPA certified laboratories with over 60 individual tests, repeatedly showing complete or nearly complete removal of ecoli, fecal coliform and coliform bacteria. The turbidiy of the output on the larger container filters is excellent, meeting or usually exceeding drinking water standards. These larger filters also remove hydrocarbons from harvested roofwater runoff from an asphalt roof.

3. Flow rate: A slow flow rate is absolutely necessary to maintain maximum purification. The slower the flow, the better the output. It is better to put up with a slow flow rate and have lots of storage, than to have a rapid flow rate just because it is convenient. These filters do not turn on and off like typical suburban homeowner’s plumbing fixtures supplied by public water systems. If a small diameter container is used (something like 5 or 6 inches), then the flow must be very, very slow like maybe 1 or 1.5 cups per hour; or there will not be enough contact time between the water and the grains of sand. This contact time is what facilitates the purification.

There are two ways to describe “flow rate”. One is by using numbers to indicate how fast the water moves through the sand bed (sometimes called “hydraulic loading rate”). The other way is to simply state how much volume of water flows out of the filter in a given amount of time. These are two very different actions. A basic explanation of flow rate is here. For the 5 gallon filter with .15 mm effective size sand, the flow should be no more than a drip like a leaky faucet about 1/2 to 3/4 of a gallon per hour and that is absolute maximum. For the 55 gallon, or the 65 gallon barrel filter, with .15 mm effective size sand, The flow should be about 7 gallons per hour (these flow rates are for a “ripened” filter) Note that all slow sand filters will start out with a much greater flow rate than they will have after running for a while. This is because the schmutzdecke gets thicker and presents more resistance to water flow.

4. Turbidity (the cloudiness of input water):
Water that is cloudy, muddy, or water that has lots of particulate matter in it will clog a slow sand filter within days, or hours. You can’t just dump mud puddle water into a slow sand filter and have it magically come out pure; and maintain a usable flow rate. Keep the water that goes in reasonably clear, pre-filter it with coarse sand first if your source water is turbid. A more detailed explanation of turbidity issue can be found here. If your input water looks like unfiltered lemon juice, it will clog your filter within a few days or weeks.

5. “Cleaning a slow sand filter: 
Clean your filter by “wet harrowing” it. There is no need to replace the sand under normal operating situations. Even if you clog it up you can still use wet harrowing to “clean” it. To wet harrow your slow sand filter, temporarily plug the output pipe so water does not flow,  then gently agitate the water inside the filter just above the top of the sand to stir up the excess accumulation of substance on the top inch or so of the sand. Do this until the water on top is filled with muck,  do not forget to plug the output pipe or the mucky water will just flow right down and contaminate your filter (we made this mistake once) and then carefully drain off the mucky water and add fresh water. Do this without excessively disturbing the sand below about 1/2 inch. The less the sand is disturbed the better. Do this until the water is clear. Then open the output pipe and let the filter run for several days to restore the biological layer. Do not ever “backwash” your filter. You will destroy it. Backwashing is for rapid sand filtration only. If you backwash your slow sand filter, you will mix the gravel at the bottom with the sand and the layers of sand associated biological layers will be destroyed. This is a very stupid thing to do.

6. Recirculation:
During dry periods where no input water is available, always have a reserve of unfiltered input water, and some filtered water to mix and recirculate through your filter until the rainy season returns. Water must run through these filters continuously, or they will become dormant and will not filter water until they are run for several weeks or longer. If they are left un-attended too long you may have to start over with them.

7. Freezing weather:
These filters will not work if they are frozen. They work marginally at 32 degrees F if the water keeps circulating through them. Don’t glue the pipes, they will crack if they freeze. If the pipes are not glued, they will just be pushed apart by the expanding water, much like a freeze plug in an automobile engine, instead of cracking the pipes. The expanding water has to have some place to go. I’ve been through this for the past 7 years. The first year I made the mistake of gluing the pipes. They were destroyed.

8. Add the sand to the water:
When putting one of these filters together, put water in the container first, then add the sand as you go, keeping the sand under water at all times. This is to prevent air pockets from forming in the sand, and to allow for testing the container for leaks. It is easier to drain out water, than it is to shovel the sand out of the filter. If air pockets form, the filter will not work until the sand is removed, cleaned, sterilized; and then put back into the container.  Don’t just fill the container with sand and then put water into it. Even if you have wet sand, air pockets can still form.

9. Wash the sand and gravel completely:
The more you wash the sand and gravel, the faster you will see a “clear” output from your filter. Wash the sand and gravel (before you put it into the filter) until the water comes out clear. This may take lots of water.

10. Don’t disturb the top of the sand:
The water input must not disturb the top of the sand ever. Keep the water flowing in very gentle. We use a “baffle” pipe assembly to do that.

11. Location:
A slow sand filter in a 55 gallon barrel is extremely heavy, over 700 pounds when it is full of water and operating. Be sure to locate and level the filter in a spot that will be its permanent location. It is nearly impossible to move this type of filter, without emptying it and restarting it, once it is set up.
Be sure the filter sits in a place where it is secure. The supports must be able to handle at least 2000 pounds safely. Moving a filter will disrupt the sand layers and cause the filter to stop functioning.

12. Know the basic reasons these filters work:
A slow sand filter works 3 ways: Biological action, Physical straining, and adsorption.

Biological (action) predation: All water, with the exception of medically sterilized water, and distilled water, has microscopic life in it. These microbes will grow in the slow sand filter if they are kept under water and oxygen and food are available. There is a mini-ecosystem that lives in these filters. This system results in the formation of a biological film, called a Schmutzedecke (German for dirt blanket) on top of the sand and to a lesser amount, further down in the sand. Disease causing bacteria, and viruses (bad bugs) are literally eaten by this collection of microbes in the filter. All that is left is harmless minerals. Most, if not all, of the small number of bad bugs that happen to slip by the schmutzedecke will die off as they move further down in the sand layer due to lack of available nutrients.

Physical straining: Particulate matter is strained out by the sand and the biofilm on the top of the sand.

Adsorption: This is a fancy way of saying that the sand grains actually can attract small particles and cause them to stick to individual grains of sand. This is similar to but, not exactly  like , the way water actually sticks to itself due to  cohesion and adhesion.

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A counter top slow sand water filter

This filter (we call it a “micro” filter) uses a 2 liter soft drink bottle, a rubber band a plastic straw, some plumbers putty, and coarse sand and fine sand. The fine sand on the top is .15 mm effective size, and the coarse sand is small pea gravel  approximately 2.5 mm effective size. The “baffle” consists of 2 re-used yogurt plastic containers one inside the other with small holes (approximately 1/16 inch in diameter) punched in each. The total cost was under a dollar. This filter has been used to filter water for a vaporizer. The well water here has lots of iron (we assume it is iron, the well is cast iron pipe, and does rust on the outside; and there are constantly accumulating reddish brown stains on the washtub) and sediment that builds up in a vaporizer and ruins the machine in a few weeks of daily use. This filter has been is use for 2 years now. The previous post shows how effective it is in removing  particulate matter. If you look closely at the images below you can see the schmutzdecke on top of the sand. This filter has never been cleaned, and still keeps working. We will probably never “clean” it. The flow from it is extremely slow, very very slow – less than 1 cup in an hour. Most people would consider this rate of flow unusable. We are willing to wait for water to flow through the sand.  We use the filtered water from it in the vaporizer and there is virtually no build up visible yet after 6 months of use. We have not checked it for biological contaminate removal yet, however we are drinking the water from the well and have been for close to 40 years, and will not hesitate to drink the water from this filter. We do know that there are no pathogens in the well water, but there are likely other microorganisms in the well water because we do not use chlorine and never have. This filter would probably not be practical for any other use. Its pathogen removal capabilities are unknown. Since the cost is under 1 dollar, (actually all of the material we used was “recycled” so, really, our cost was 0, if you had to buy the stuff outright it would probably be about 1 dollar) it would be easier to make a new one if this one stops functioning.  Images below:



This is a 2 liter countertop slow sand filter. It filters out iron, and particulate matter from the well water we use here.



This is another view of the small slow sand filter. Notice the “schmutzdecke” on the top of the .15 mm effective size sand.



This is the filter in action. It removes iron, and particulate matter from the well water.





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It is now April 11, 2014. Filter 10a, 10b, and 10c have been running steadily for about 6 weeks.  Filter 10a uses .25 mm effective size sand, filter 10b uses .15 mm effective size sand,  and filter 10c uses .20 mm effective size sand.  These filters were inoperative for half of November, and all of December last year (2013); and all of January, and 3 weeks in February of this year because of below freezing temperatures.  A water clarity test has been done on all three filters and the results are shown below. The flow rate of these filters is very slow; about like a dripping faucet. This is the compromise necessary to make these filters work. They are totally different than commercial “on demand” filters that let water flow freely from the kitchen faucet.This is very important to know. If one of these filters is put together with the expectation that water will just come flowing out like it does from a typical household faucet; the result will be disappointment for sure.


This is the output of filter 10a as of April 11, 2014



This is the output of filter 10b as of April 11, 2014



This is the output of filter 10c as of April 11, 2014



This is the source water that feeds filter 10a, 10b, and 10c.

It looks like filter 10b is doing very well at removing physical contamination. A biological test will be done asap. All of the above images were created using an led, focused light source powered by two fully charged NiMH cells rated at 2400 milliamp hours. All of the containers are of the same type. All of the other images on this blog, with the exception of those using the red laser, use the same led light source with fully charged batteries so as to maintain consistent light brilliance for comparison purposes.

Below are some water samples: three from our deep well:  water from that well filtered by a sand filter, and water from that well filtered by a commercial filter that attaches to the faucet, and unfiltered water straight from the well storage tank;  and following that, a bottled water sample.

sand filtered water

– This is filtered well water from our deep well, after it has been through a “micro” slow sand filter that sits on the counter (more on that “micro” slow sand filter shortly.)


faucet filter water

This is the same deep well water that has been filtered by a commercial filter that attaches to the faucet.


well water

This is water from the deep well with no filtering, it is straight from the storage tank.


bottled water sample

This is bottled water









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Slow Sand filter construction

Update October 22, 2013: This filter is still working after 2 years of continuous operation. The filter has been monitored regularly, and as a result,  a potential issue with the sand has been discovered. The bottom layer is too coarse, … Continue reading

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Slow sand filter operation during dry spells

Filter 4 and 5 now have re-circulation systems installed. Both of these filters had failed miserably in April/May of this year due to lack of water throughtput, and excessive organic debris present in the input water. Since the re-circulation systems have been installed and running for 2 months, the water in both filter systems has improved tremendously. The foul odor is gone, and the water is clear again. The details follow.

There have been 5 options for re-circulating water used here. Totally manual, an electronic timer, a modified ball valve, a modified standard hose bib, and a drip irrigation timer.  All five work. The modified standard hose bib was the most difficult to set up and the least professional – it is not shown, even though it does work.

The manual method (adding water from a bucket filled by a hand operated pitcher pump) and the electronic timer will work with a non-pressurized system. The manual method is the most time consuming and requires daily attention.

The electronic timer switch is the Amico DC 12V Digital LCD Power Programmable Timer Time Switch Relay 16A      sku 40037612     This timer will handle 16 amps.  We are also now testing out a PV array set up to charge and run small dc motors of the size used in the pumps on the recirculation systems shown here. So far, a 50 watt PV array produces waaayyyy more power than is needed to keep the motors running during the summer months when there is little or no rainfall. The recirculation is not really needed in the fall, winter, or spring, so the lack of sunshine is irrelevant.

Much more info as I get time. . .   .   right now “I got all the freaking work I need”.

modified ball valve

This is the ball valve. It is in use on filter 4 along with the electronic timer, for test purposes only. Either this or the electronic timer will work alone. The extended arm on the ball valve allows very fine adjustment of flow rate.The electronic timer is not needed, we are just testing it out.

programmable timer

This is the programmable timer. It will work with or without a pressurized system. It just turns the motor off and on at specified times. Up to 17 choices in 24 hour time period. This is in use with filter 4. So far the timer works like a charm. The “manual” button allows the water to be turned on and off anytime without disturbing the programmed times.

timer circuit

this is a schematic of the timer circuit hookup. The battery symbol represents the 12 volt power supply for the motor and the timer. The timer must have the power supply hooked up before the relay inside it will function. The capacitor is necessary to keep the relay contacts from being burned by arcing as the motor has significant inductance.

This is the schematic of the filter 4 system that uses flow regulation and flow frequency control using the electronic timer switch.

raindrip timer

This is the raindrip timer. It works with a pressurized system. This is in use on filter 5. It is set to allow flow for 1 minute every hour on the hour.

This is the schematic of the recirculation system with the raindrip timer.

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Biological water filtration with sand (why does it work?)

Biological sand water filtration (slow sand water filtration) works mainly because of living things we can’t see with our eyes. If water flows slowly enough through sand, it can be cleansed by these living microscopic organisms with help from gravity and small particles of sand.

To more clearly understand why (and how) biological sand water filters work, know that water is recycled “naturally” by its interaction with living organisms, ultraviolet light (sunlight) , and physical filtration through earth (usually called soil or dirt) and porous rocks. Be aware that this earth is alive all over and that microscopic life exists almost everywhere here on this planet. Lots of these tiny organisms are in water and most of them are harmless to healthy people. Without these organisms, we would not survive. Understand that without water, there would be no life as we know it here on this planet. To be comfortable with the idea that water can flow through “dirt” and come out clean; a new way of thinking may be necessary for lots of people.

To attain this mindset, try to stop thinking of the stuff on the top 15 inches of this earth as “dirt”, or re-define “dirt” (maybe referring to industrial pollution as “dirt” would help); and remember where our food comes from – its NOT the grocery store. All of what we eat depends on land and water – the surface of mother earth. Potatoes, radishes, carrots, garlic, onions, beets, yams, sweet potatoes, shallots, ginger and peanuts, to name just a few, all come right out of the “dirt”. Ok, lets stop calling mother earth “dirt”. All come from mother earth. We may buy them at the “grocery store”,  but they all come to us courtesy of mother earth.

In a biological sand water filter, micro-organisms, most of them harmless, grow and cling to the surface of sand particles inside the filter. As water flows slowly through the sand, these organisms form a biofilm that traps and consumes other micro-organisms including those that make people sick. In recent history (the past 150 to 200 years) it has been known (documented) that this type of filtration works in man-made filter systems. In the past 20 years, scientists have discovered a lot about why and how it works.

Some of the details are in the rest of the pages of this blog, and may also be found easily on the internet by doing a search for “slow sand water filter”.

My references can be found here:

and here:

Also included my references:

7 years of experience building and testing slow sand water filters documented here:

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