About this rainwater harvesting blog

Update August 26, 2019:

After a devastating winter (2018-2019 : 2 feet of snow, then ice) we have finally finished most of the repairs to the various systems and structures here. There is still more work to do.

Again I want to emphasize this is not a political blog. If you post political opinions here they will be marked a such, and may or may not be approved. Inflammatory or derogatory comments will not be approved. Comments backed up by facts will nearly always be approved. “Alternative facts” are not “facts” they are lies.  With the new administration in place there are very likely to be new laws put in place regarding rainwater harvesting. If you have a comment regarding any such new law, please, PLEASE, back it up with a credible link to your source. Make sure the law is relevant to rain water harvesting or slow sand water filters.

Roof water (rainwater) harvesting along with slow sand filters will soon become a necessity rather than a curiosity. This blog is an attempt to increase awareness of water supply options available to the individual, and provide a means for discussion. If you are located in the Pacific northwest part of Washington state, and would like help setting up a rain water /  roof water filtering system leave a message at the bottom of this page in the comment space with your contact information, and we will get back to you as soon as we are able.

The work described here takes place at the edge of the foothills of the Cascade mountains in western Washington state, U.S.A.  about 30 miles northeast of Seattle Washington. All of the testing and work done here is based on the environmental conditions here in this small part of the world. The image at the top of the blog page is Eagle Falls, which is located in the Cascade mountains.

The information posted on this blog by the author regarding the design,  construction, and operation of small slow sand water filters is based largely on actual experience, which has been ongoing for 11 years now; and will continue as long as physically possible. The websites slowsandfilter.org,  shared-source-initiative.com/biosand_filter/biosand.html and   roofwaterharvesting.org are connected with this blog through the same author and similar topics. The study of existing peer reviewed scholarly articles along with documentation from other websites is also used. Links to these sources can be found here, and here.  The tests on water flowing into and out of the filters are done by EPA approved laboratories and the results are posted on the websites noted in the links above. Neither the author, nor this blog are connected with any religious or political group(s) or organization(s), financially, or otherwise. We now need to look for some assistance in funding this site, as costs have gone up exponentially. Shortly, we hope to be offering for sale, a compilation of our most important work over the past 7 years in PDF format. This will help keep this site, and our others mentioned above available in the foreseeable future.   

Please keep your comments and questions relevant to rainwater and/or roofwater harvesting, biological sand filters and sustainable water purification practices studies. If you have information that shows disagreement with any post on this blog it will not be deleted, providing
you show evidence for your statements. Opinions not backed up by evidence will be marked as such.

Important: Do not drink the water from any of the filters described in this blog or on the following websites associated with this blog without having the water tested by your local health department. Know that each owner of a filter is totally responisble for its proper operation and water quality. Even if a filter is built exactly like the ones shown on these websites, it is still possible for it to produce contaminated water. This blog, and the 3 websites associated with it, and any communication with the author do not make water 100 percent safe to drink. Public water systems are monitored by professionals and still there are contamination outbreaks that do occur.

Please, do not confuse the devices described on the above mentioned websites with the “Biosand filter”. The Biosand filter is an entirely different design, and has been thoroughly tested in the field and in use. The Biosand filter is NOT EXACTLY the same thing as the filters studied on the websites associated with this blog.
You have been advised.


28 Responses to About this rainwater harvesting blog

  1. Patrick Fallon says:

    Hi, really inspired by your blog, and your instructions of how to make a slow sand filter. I am writing to ask about the pitch of roof, as I didn’t quite understand on the specific details section. I am an architecture student and live in england, UK and am trying to integrate this system into a building I am designing. The site is in medieval Salisbury and the yearly rainfall is 40inches. I calculated that if i had a series of small study pods of 13sq feet over a year they could collect about 900 pints each. Would a pitch increase the need for more roof area? this was what i didnt understand. Also is it possible to have a series of small personal sand filters in these small rooms, or is it always better to have a large storage tank that can be distribited. thanks Patrick

  2. admin says:

    The part about the pitch of the roof is a bit ambiguous. For a given fixed perimeter or square footage of floor space, as the pitch of the roof increases, the total area of rain catchment surface increases. So more gallons per inch of rain becomes available. For example for a slope or pitch of 4/12 (4 units rise and 12 units run) a certain given amount of runoff is available. If you increase the pitch of the roof to say 8/12 then there will be more surface area of roof to catch water.

    Probably one large filter with a single storage tank would be the best option, as there will be less likely hood of contamination.

  3. Rebecca says:

    Hi, David. We had exchanged links a while ago and I wanted to update you that my popular Build Your Own Rain Barrel website has moved to:


    Looks like it’s on this page at least of your site(s): http://www.shared-source-initiative.com/biosand_filter/biosand.html

    Thank you, and Happy Watering!

  4. admin says:

    Thank you Rebecca. Getting the barrels set up is the first step. If everyone here in Seattle had rain barrels there would be a lot less (massively less) pollution running into lake Washington, the rivers, and Puget Sound. I did update the links on the original website, and of course it will show up here also. There are two other sites associated with this blog, I suppose I could put links there too.

  5. Kevin says:

    You mention that the living layer of the filter must always be submersed, but does the water need to be continually aerated/recirculated? If so, do you have any recs. for the recirc. pumps and power sources? You mention in several places that the water from these filters should not be consumed. I was thinking about using something like this for an emergency water filtering system, but is there something else I should be looking into? I’ve seen the slow sand filters being touted in third world countries as a way to filter water and improve human health. If their water is consumable, what might they be doing differently than you that makes their water consumable? You also mention that some of your filters have frozen. What steps are taken to “restart” the filters after they are frozen? Is the living layer completely destroyed, or does it go dormant? Thanks for all your time.

  6. admin says:

    A good source of information about filters in places other than the U.S. can be found at
    this website regarding the Biosand filter.
    These filters have a design that has been tested by health officials and is known to work.

    There are (at the very least) thousands of pages of studies regarding the “living layer” in a “slow sand filter”. The website slowsandfilter.org has a page with
    a collection of scholarly articles describing, among other things, the known characteristics of the biological activitty in a “slow sand filter” . These studies would be the most authoritative sources of information regarding the biologically active layer of sand.

    As far as the biolayer being frozen, the only step I have taken so far is to wait for the filters to thaw out and start flowing again.

    I cannot tell anyone if the water from any filter is ok to drink. Local health officials are the final authority on that.

  7. Brian says:

    I am in process of building a 1200 gallon concrete rainwater cistern at my home in Portland, Oregon. It will be cut into a hill, so 3 sides against / partially against the soil. A friend questioned whether freezing water would damage the concrete seal or the blocks. Any thoughts or experience?

  8. admin says:

    Hi Brian. My thoughts, for what they are worth . . . here goes. Last winter it got down to about 15 degrees here and our cistern did not crack, 1/3 of it is above ground all the way around and it was damp on the outside and leaking on the inside. There was no obvious damage. My best guess would be that if water gets into the cement and freezes there it will crack. Freezing on the outside should not hurt it unless the water can penetrate into the concrete. I would make sure the cistern is sealed completely from the outside as well as the inside. It will have to get really cold for a long time for the water to freeze inside a concrete cistern and I don’t think it will get that cold too often here on the west coast. That said, we did have that cold spell several years ago when it got down to about 5 degrees here. I’m not sure about the Portland area. I hope your cistern works out ok for you.

  9. Ben says:

    I was directed here from [http://www.shared-source initiative.com/biosand_filter/contact.html] I don’t know how to contact you otherwise, but I’m conducting a few experiments on alternate water filtration techniques for school, and I need to cite sources. If you could email me your info, I would appreciate it. If you would like more info on my project, feel free to email me.

    Ben H.


  10. admin says:

    The works cited page on the shared-source site is :
    The works cited page on slowsandfilter site is :

    To cite my work just follow the attribution requirements on this page:

    and this page:

  11. James says:

    To Author,

    I absolutely love your DIY site, http://www.shared-source-initiative.com/biosand_filter/biosand.html

    My only real question is this: Where do we get those materials?

    I’ve tried going to certain stores but no one seems to carry the PVC or the sand materials you described. In fact, getting the PVC joints seems impossible.

    Who are the distributors for PVC parts?

    Again, create site and thanks for blogging about it.

    Try Lowes, or Home Depot. Also, your local hardware store should have pvc fittings. You can order them online, too. Either Lowes, or Home depot will order sand for you. You can also get sand locally and sift it yourself.
    Posted by Filter Guy

  12. Jim in Seattle says:

    I’m interested in setting up a system like this for vegetable gardening and as an emergency water supply. I’m putting together a parts/cost list. I’ve been unable to source the “Target” fine sand or silica sand online. Would I need to contact a pool supply store? And for the coarse (or ungraded) sand: will regular playbox sand from Home Depot/Lowe’s work?

  13. Orpheus says:

    The “Target” sand is available from McLendon’s hardware.
    Sumner: 253-863-2264
    White Center:206-762-4090
    Woodinville: 425-485-1363
    Kent: 253-850-2722
    Puyallup: 253-536-6560
    Renton: 425-235-3555
    You will need to ask them specifically for the “Target Filter sand”. Also, the Renton store has a very nice selection of sand from the “Unimin” company. I use the .15 mm effective size sand in several of the filters here. There is an outfit in Renton called “Manufactures Mineral Co.” They are located at:
    1215 South West Monster Road Renton, WA 98057
    (425) 228-2120
    They have .25 mm effective size filter sand in 100 pound bags.

    Salmon Bay Sand and Gravel, in Seattle (Ballard) has the Unimin .15 mm effective size sand in 100 pound bags. They will load it for you.

    The simplest way is to buy sand that is already sifted. However; if you use the “Play sand” from Lowes, you will need to sift it using stainless steel wire cloth. The play sand won’t work without sifting because it has too much inconsistency in the size of the grains – it has lots of very fine and lots of coarse grains. The stainless steel wire cloth is available from Grainger. You’ll need to make a frame out of 2X4’s or 2X6’s to hold the wire cloth. I would use 40 mesh and 60 mesh. Discard the the sand that won’t go through the 40 mesh, then put the stuff that goes through the 40 mesh on to the 60 mesh and keep the stuff that does not go through. The 40 mesh has larger openings than the 60 mesh.

    Update August 13, 2012: After purchasing the “play sand” today, and looking at the wire cloth, it appears that 60 mesh will be way too fine to be used
    on this sand. I will try some sifting asap and post the results as I get time.

    August 14, 2012: The “play sand” is not uniform size, and is a real pain to “sift”. I tried it today, and spent a lot of time fooling around with a 50 pound bag of sand, only to end up with about 15 pounds of uniformly sized washed sand, which was very fine and actually looked good, but the effort was great and the reward tiny. To make a long story short, If you don’t have to sift sand – don’t.

    On the other hand, the sand I ended up with, probably will work for the top “fine sand” part of a slow sand filter, but it will take at least 10 bags of the play sand to get 100 pounds of the fine sand after sifting it, and; if the mixture from the manufacturer of this sand varies even slightly, (as it might since it is not being “packaged” for filtration), the end result could be entirely different; and furthermore, the sand requires huge amounts of water to wash it. To get 100 pounds of this sand sifted and clean will take hours of work, and at least several hundred gallons of water. The mesh sizes I recommend are too fine to end up with .25 mm effective size sand for the bottom part of the sand in a small slow sand filter. 30 mesh might be a better choice. Also, note that different manufactures have different ways of referring to their “mesh sizes”. If you sift this sand dry, ABSOLUTELY WEAR A DUST MASK. THE DUST FROM THIS STUFF IS NASTY- I CANNOT STRESS THIS ENOUGH – WEAR A MASK. Wet, however, it is fairly harmless, with the exception of drying out your hands.
    Dave T
    Snohomish, Wa.

  14. filter_guy says:

    In response to the comment above, by James (June 16, 2012): Try Lowes, or Home Depot. Also, your local hardware store should have pvc fittings. You can order them online, too. Either Lowes, or Home depot will order sand for you. You can also get sand locally and sift it yourself.

  15. Celismar says:

    Hello good morning,

    My name is Celismar Oliveira, I am student of Agronomy at the Federal University of Lavras (www.ufla.br) in Brazil. And now we have gone through several water crises in my university for example has entertained the possibility of break in classes due to lack of water. And when I was doing research on adsorbent capacity of activated carbon was when by coincidence I came across your project sand filters. Particularly found it very interesting and can be affordable to many low-income people.
    Well, my interest is in design in Auto CAD, because I was weighing in using your model, but with some adjustments, such as using a type of activated carbon that we can get from cane sugar and ultra violet lamps to be used in the first process. Well, but that’s just flat. If you could count on your cooperation would be great if you have the design in Auto CAD’ll thank me if you can provide. Already I want to congratulate for the design and creativity, I believe it is the stock so that the world needs.
    I’m disposal for more information.

  16. Stephen says:

    Hello and THANK YOU for all of the great info!!
    I live NNE of Seattle out in the woods with a substantial creek on our property. We do not have city water and set out to provide our household water with rainwater catchment. I have screened gutters on 468 sq ft of metal roof. I put in place the following (in order of installation):
    First flush diverter
    75 micron screen
    25 micron felt “sock” filter
    2 – 300 gallon IBC totes
    Water pump
    Check valve
    5 micron pleated filter
    .5 micron carbon filter
    26 watt UV water sterilizer
    12 gallon pressure tank.
    Pressure switch (controls pump)

    The resulting water has been quite good. Unfortunately the 5 micron and .5 micron filters do not last for very long. It was tolerable when this was my part time residence and I went to the laundry in town.
    Now that I am here full time and have started using my clothes washer (PIG!!) my filters are lasting only a few weeks.

    I am pondering what the best approach to resolve this would be.

    One option would be to change my filters to allow larger contaminates to pass and add additional filtration to the kitchen sink for drinking & cooking.

    Another option I have considered is to place a bio-sand filter between the 25micron sock and the IBC totes to further filter the water before it hits the 5 & .5 micron filters.

    I would also like to have the ability in place to use water from the creek in case of emergency. The creek is a fast moving body with significant volume. In the summer it is clear enough to see the bottom well at 12+ feet depth. In the winter & spring it is quite turbid.

    Wow… That turned out to be a bit longer than I had expected…

    What can you suggest for my circumstance?



  17. filter_guy says:

    Hello, Stephen. Thank you for taking the time to comment here. It will take me some time to organize info for a good reply. In the mean time, I would highly recommend a slow sand filter in your system the way you describe it. The water from one of these filters can be of very low turbidity, and of very high quality. Your 5 and .5 micron filters should last a long time with that kind of setup. I’ll get some info together for you and post it a little later on.

    That system you have there sounds really good. Without actually seeing your system I can only make educated guesses at what might help. Slow sand filtration added to that system would probably help. The turbid water from the creek might be a problem, depending on how much turbidity there is. Much over 10 NTU’s will clog a slow sand filter quickly. You may need a pre-filter of some sort in the case of highly turbid water from that creek. I spoke with one person several years ago who planned to use an “upflow” gravel filter at the beginning of his system’s filtering sequence. If the water looks like unfiltered lemon juice, it is too turbid for a slow sand filter. You may need to experiment with different gravel sizes to find out which one works best. Perhaps even very coarse sand would make a good pre-filter. I would
    suggest using a 55 gallon barrel filled with the coarse sand or gravel for that kind of filter.

    Be sure to check out our 3 other websites:

    A slow sand filter can be made to operate from a pressurized system using a float valve as a flow control device and it sounds like you have pressurized water to your system following the water pump. You might be able to use a slow sand filter in your system where you have pressurized water available. We use slow sand filtration here with pressurized water as the input to the filters. Take a look at this webpage on one of our websites:

    I can tell you that the filters shown on the website at slowsandfilter.org work nearly flawlessly for us here (extended periods of freezing weather have been a problem). We have pressureized water from a shallow well feeding both of the slow sand filters you saw at the previous link. The float valves in each of the
    filters automatically shut off the water when the filters are full. As long as water is allowed to flow out of the filters the float valves will keep the water flowing at the rate necessary to
    make the filter function, without the problem of overflow. If the output of the filters is shut off, water does not flow and every thing stops until water starts flowing from the filters again. The system works flawllessly. If you wanted to use a system like this, you would probably want to use
    a large holding tank to store the filtered water. It need not be pressurized, just sealed so it won’t overflow. You could use a float valve in the storage tank also, that way when the tank fills up, it will automatically shut off the flow from the filters which will cause them to stop when they fill up. Then all you need is a small capitive air tank hooked up to a pump that draws water from your filtered storage. This is the setup we have here, only our “storage tank” is a 2500 gallon concrete cistern. Its our back up water supply. The final touch would be a UV filter like the one you have there. The water that the two filters produce is better than our deep well water. I have not “cleaned” (wet harrowed) the two filters at all. No need to. The flow has stabilized after 3 and a half years of continuous service.

    A note of caution: if you use float valves, be careful when turning on the pressurized water if the water level in the filter is low. The pressure may disrupt the surface of the sand. Start out slowly, then when the filter has filled significanly, you can then increase the flow/pressure to maxium. As the filter runs on its own, water flows only very slowly because the float valve starts immediatly after the water level drops even 1/4 inch or less and the flow rate at that time is not disruptive to the sand surface because it is so slow. Keep the “baffle” pipe well above the sand surface. Ours are about 4 inches.

    I’m not sure which creek you’re on. I would recommend checking upstream for any kind of potential pollution, only because I do not know
    your situation. If you’re downstream from anyone using glyphosate or any other kind of herbcide or pestcide; or if there are any private septic systems upstream from you, its highly unlikely that a slow sand filter will be able to take all that junk out – all of the time. Keep in mind that the amount of
    pollution can vary drasticlly from time to time in a creek. If you are sure there is no pollution upstream then your only problem will be microbes and turbidity. Highly turbid water will
    plug up a slow sand filter within a few days, a few hours or even minutes, depending on the severity of the water’s turbidity. Your pre-filter should be able to bring the turbidity level down to about 10 NTU’s or lower. Most pathogens are easily removed by a properly functioning slow sand filter. Having a UV filter in your system as the final stage of “filtering” is a very good precaution in case some bad bugs happen to slip by the slow sand filter. Our exeperience here has been that the coliform usually slips into the system after the slow sand filter output. That is, the contamination occurrs in the storage tank or in the output
    pipes from the storage tank.

    Also note that, based on our experience, there may limits to what a single slow sand filter system can do. In my humble opinion, it would be possible to overwhelm any system if the bacteria or virus level present in the input water were to become too
    high. We have tested one of our systems here at 50,000 cfu’s per liter at the input, and our filters here at approximately 30,000 cfu’s per liter, and they take it all out. Anything above that we have not tested.

  18. Crystal Rogers says:


    I will be visiting the Seattle area July 7 – 14. Is it possible to visit/tour your facility? I’m originally from Seattle, but now live in Lisbon, Portugal and I’m interested in creating my own sswf using rainwater.


  19. filter_guy says:

    Yes, it is possible to visit the location here and observe the filters in action; however, we ask that you have an appointment before visiting. An appointment can be made by emailing us with a request.

  20. Jack says:

    Well this is all very interesting however it seems to me a rather daunting task to put this all together given my present time constraints.
    I will await the info that I purchased and go from there.
    I plan to harvest rain water and my cabin is located in Western Washington with a year round creek. Is it possible to receive enough rainwater to serve a full time resident. Will I need to have the creek as a back up water source? Is it legal to draw water out of creek?

  21. filter_guy says:

    Thank you for the comment, Jack.

    If you are west of the cascades and your cabin has a roof with at least 200 square feet of surface, and you’re not buried in trees, and you get at least 30 inches of rainfall a year average; there should be way more that enough run-off from the roof of your cabin to supply 1 person with a year’s worth of water for purposes other than direct consumption. The issue will be storage, and secondary disinfection. Summers can get pretty dry here, as you probably know. I would suggest at the very least 2000 gallons of storage. As far as potability, that is a separate issue. The water that runs through the slow sand filters we have here is not used as potable water, and we cannot guarantee the quality of the water from any slow sand filter we design that is not maintained here onsite. As with a private well, at any point in time, the water from any of the slow sand filters we design may become contaminated, and the water quality in either case, is totally the responsibility of the owner/operator, and is used at their own risk. Water must be tested to be certain of the quality. One way to insure the quality of your water is to use a U.V. filter on the output water from the slow sand filter. Keep in mind that the turbidity of the water that runs through a U.V. filter is critical to its proper operation. Water testing kits can be found here. Another method of disinfection can be the use of chlorine. The biggest issue with chlorine is the way it interacts with residual organic material. A slow sand filter removes most of that type of contamination, so the use of chlorine is not as toxic as it is when used in conjunction with rapid sand filtration.

    Regarding a back-up water source, your usage will determine that requirement.

    As far as drawing water from a creek, I have not done any research on the legality of that practice in Washington state, so I cannot speak to that issue right now. My only research has been on the legality of rainwater harvesting, which is legal in Washington state.

  22. Kathy says:

    I am interested in having you consult me on building my system can you please contact me at ******************

  23. filter_guy says:

    Kathy, we’ve sent you an email. Your email address is NOT posted here.

  24. Catherine Wells says:

    Rainwater Harvesting reduces the damage to our creeks, water habitats and organisms caused by stormwater runoff.

  25. Manoj Kumar says:

    Rainwater harvesting is another way to use rain water for future.Here is Rainwater Harvesting website for India.The main purpose is teach about rainwater harvesting and other water related matter so that we can have a sustainable water supply for generation to come.This website is full of information about rainwater harvesting fundamentals, future events and programs, and locations.

  26. Bill Dryden says:

    I live at the 4500 ft level, above Fresno CA. I purchased a used 1,500 gallon tank – that did not leak. I installed one snow gutter that covers a 15 ft by 84 ft roof, with two downspouts. I filled up the tank with 1100 gallons (capacity 1500) with 1 1/2 inches of rain and realized I needed another tank. I purchased another 1100 gallon tank. Then had another 1/2 inch of rain and filled up original 1500 gallon tank. I am sure that the extra 1100 gallon tank will fill up with the next storm system of 1-2 inches. I am amazed at the accumulation of water. I have gravity flow to my garden, twenty five feet below, with plenty of pressure. Life is Good!

  27. Charis Boissevain says:

    Thank you for the amazing article & for the valuable information you have shared. I am looking at installing a Rainwater Harvesting system on our property & this has been very helpful. Best wishes, Charis Boissevain

  28. henry says:

    Thank you for helping spread information on rainwater harvesting, we just started our rainwater harvesting company in Seattle to contribute to the RainWise program and support water conservation and stormwater management efforts. We are at https://www.rainwatersystemsseattle.com if anyone would like more info

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