Rain water harvesting and slow sand water filters

There have been some questions regarding toxins leaching from the pvc piping used in the filters described on the website referred to in this blog. Because of construction requirements we are limited as to our choices. Copper pipe has adverse effects that are already known and established. I have done some research on the pvc pipe issue. There are contaminants in water from pvc and cpvc pipes. The levels vary from barely detectable to detectable, but the chemicals are quite toxic.:
www.mindfully.org/Plastic/Organotin-EP.htm
That said, copper has its own problems: www.drlwilson.com/articles/copper_toxicity_syndrome.htm
And chemicals added to water compound the problem
I guess pick your poison! As far as toxins, perhaps poly-pipe, stainless steel, or bamboo would be the best choice, followed by cast iron pipes. These have their challenges as far as construction. And bamboo shoots contain cyanide:
www.inspection.gc.ca/english/fssa/concen/specif/fruvegtoxe.shtml
Also, bamboo will present considerable challenges in freezing weather and in construction – for example how to get the bamboo through the container and seal it? Bamboo is strong, but it is organic and will eventually decompose.
The situation regarding chemical toxins in water from pipes is very complex. The nature of the contamination will depend on the ph of the water, the temperature, the mineral content of the water, the length of time the water is in contact with the pipe, the types of bacteria in the water, and the disinfectants used, Probably the best option would be stainless steel or tempered glass. Stainless steel pipes would be way too expensive and glass, even though it be tempered glass, would be impractical. Poly pipe is probably the best choice if a person is concerned about toxins:
www.plasticpipe.org/municipal_pipe/potable_water.html
Well, that is, until a way is found to identify toxins that leach from HDPE plastics! It is important to realize that all water with the exception of distilled water, has more than just H20 in it. That pristine natural spring, high in the mountains, away from all the “toxic” stuff, has dissolved minerals in it. There is no way around that. Most of those minerals are harmless, as far as science knows. Some of them are not. It just depends on the concentration and the type. Until we know all possible contaminants and all possible effects I will probably continue to use pvc pipe.
However, I am 62 years old. Someone with children will probably want to use the stainless steel pipes, in fact they may want to have their house re-plumbed with stainless steel – however then, they should be prepared to take out a second or third mortgage to have that done. I would suggest to those concerned: a good idea would be to check into where your water comes from and what pipes bring it in to your house – most likely it is pvc. If it comes from a reservoir, the pipe may be anything and anything may be in the reservoir. Some reservoirs are sealed with petroleum derivatives. My educated guess is, that it is probably possible to make pvc piping safe, but doing that will reduce profits and make shareholders unhappy.

Just a short note here. The “pond filter” mentioned on the slow sand filter site slowsandfilter.org has been working for 15 weeks. The thing is put together without the elaborate “baffle” pipe assembly and using .35 mm effective size sand. It has just a flat piece of slate rock sitting on top of the sand that the input water splashes on instead of using the baffle pipes to keep the water from disturbing the sand surface. The filter’s top sand surface remains undisturbed. The water is clear and the birds love it. A coliform test will go in shortly. Since the water is always splashing and completely recirculated from the bottom up every 24 hours, there are no bad insects like mosquitoes breeding in the water. The whole thing, including the small fountain pump cost under 100 dollars. The main purpose here is to determine if this design is effective in removing coliform bacteria.

After reading website after website on how to build a biological slow sand filter, I have come to the conclusion that people need to learn more about how they actually work. Here are 50 references to studies on slow sand filters, roof water harvesting and related information
Read them. Most of the studies have 50 or 60 references to other studies on the same topic, that makes hundreds of studies. Read those too.

Now let’s clear the air about the ninnies who throw around their “beliefs” like they are facts. I could get into a long philosophical argument – with people who deliberately prevaricate science – about the validity of scientific inquiry and peer reviewed scientific writing. I have seen this ludicrous situation between “climate change deniers” and those who back up their claims with research that has thousands of other people supporting it; and it makes me sick. Here’s the deal. People do studies; they know what works from experience, watching for results, and the use of high tech equipment. There are hundreds of studies ( some of them are listed on the above page ) that have been done on biological sand water filters (slow sand filters, bio sand filters). These studies have used instruments that can measure and detect things that are impossible to detect with the human eye. The studies are done by people who KNOW what they are doing and they KNOW HOW TO USE THE equipment. There are thousands of biosand filters in use around the world (mostly outside of the USA) and they work. The information in these studies I have mentioned is available for anyone who has access to a public library or a public university library. Now, it is true that there are lots of people who don’t have that access. It is therefore the responsibility of those of us who do, to accurately report the information from the studies, and to NOT distort the facts. There are those who throw some sand in a bucket and call it good. I have no problem with this and sharing ideas and experience is a very good thing, but so many of them come across as if they are the final word with nothing but bluster and fancy graphics to back it up. PLEASE before you come up with your own ideas about how the thing works, READ THE STUDIES, and learn some biology and some science and take your output water to an epa approved lab and have it tested – and learn what to test for. Now enough of that.

A biological sand water filter works because of microscopic life. This life consists of bacteria, zooplankton, diatoms, and algae. There are hundreds of different types of each.

The top 5 – 10 centimetres of sand are the most active, but biological activity occurs as far down as 40 centimetres from the surface of the sand; and, over time, naturally formed layers of sand make the filtering process more effective. The sand must be at least 65 cm deep ( about 25 inches) . The organisms that make a slow sand filter work are aerobic and aquatic- they must have oxygen and be under water to survive. Most of these organisms are harmless to people. Because they are alive, they must eat something to survive. They will ( and do ) consume pathogens ( bacteria and viruses that make people sick ) in water. All that is left in the water is harmless minerals. A layer of organic “goo” forms on the surface of the sand – it is not necessarily visible. This traps particulate matter and living organisms. The water that emerges from a functioning slow sand filter is purified – pathogens are REMOVED not just killed. A biological sand filter is not the end all solution to clean water supply. And there are problems with these filters. Those problems are also listed in the studies, and also on this page:
http://www.slowsandfilter.org/ssf_faq.html
Read them. Then build your filter and test it.

I guess this will be kind of a rant. Sorry, but it must be said, besides I have pneumonia now and have to keep from doing a lot of physical work. People are just too darn complacent. Somebody has to fire people up. So here goes . . . . . After following the access logs for the water filter websites for several years, I have found an interesting trend. More than half of the hits are from areas outside of the USA, or from areas where there are currently issues with water in the USA. ( I’ll call these people the “enlightened” ). For example, in the US state of Georgia, there are places where water is no problem, and places where there is “drought”. These people need water NOW. However, to urban and suburban people in “the developed world” with access to the internet, access to clean water is not really a big life threatening issue. It is philosophical or theoretical – an abstract concept that should be argued in academic discussion groups, and their “rain barrels” are painted stylish novelties to be outdone by competitive neighbors. ( I’ll call these people “clueless” ) Here’s the deal: Clean, pathogen free, poison-free water is a human right, not to be bought or sold as a commodity. The sooner the developed world gets that through their collective thick heads, the better off we will all be. And furthermore, there is a bigger picture here. The picture of life. Our excellent science ( I’m not trying to mock science it is a VERY good thing – it is just misused and abused ) has not yet given us all the details about life; and this fact is brought to light by the mysterious operation of aerobic life forms that exist in water and particularly in a slow sand water filter. Our science can show us that they work to purify water, but scientists still don’t know all there is to know about all the microscopic life that makes these “filters” purify, yes that is purify – remove pathogens from – water. ( Public water supply systems only sterilize water – the dead pathogens are still there when you drink it along with all the toxic byproducts created when chlorine, or ozone turn the dead organic compounds into carcinogens ). Wetlands purify water in a similar fashion to slow sand filters. And, yes ( as the “clueless” will chant ) over a period of tens or, hundreds or thousands of years, the dense rock underground will physically filter water, but that is of no use to us NOW. Biological purification of water takes only days and it works.

For city dwellers this all may be hard to understand. Water is all around. Drinking fountains are all over the place. If you’re not on a well, you just “pay the water bill” and drink on, getting the water to you is someone else’s problem ’cause that’s what you pay for. WRONG. DEAD WRONG. The water bill is nothing but a token. Those of us who get our water from a well understand this. Your water supply is CRUTIAL, expensive and a BIG DEAL. Water is absolutely necessary for life, without it we die quickly, as a result there are tremendous guaranteed profits to be made selling water. Just look at the “bottled water” industry. This is compounded by the undeniable fact that disease is easily transmitted by water, and because of this, water supply purity MUST BE assured. This sort of adds credence to the old saying “you never want a drink till the well runs dry”. Now, the “clueless” will correctly say: “There’s no problem, the earth is huge and there is enough water to last forever, besides, it evaporates and that cleans it. It spends time in the oceans then evaporates to rain and that cleans it. We don’t need biological cleaning. Sunlight kills all viruses and bacteria in the rain clouds anyway.” The problem is that man is way too anthropocentric. The “earths” problems are not the same as “human” problems. Plastics break down in, well, several hundred to several thousand years – a problem to us but not really to the earth. Radioactive material breaks down after 30 or 40 thousand years, a huge problem to us but, not to the earth. Water polluted with heavy metals may eventually clean up but not in time for people to use it. Even petrochemical pollution will eventually break down – not a big problem to the earth, but to people – deadly. We can deny our way to the ultimate hedonistic gratification culture. Science has become so complex that it is easy and convenient to hide motive for profit in complex fact based research writing.

People die without water in 4 days. People die from terrible diseases if they drink water with pathogens in it or if they drink water that is contaminated by industrial or chemical pollution which can come from indeterminate sources.

Now all this water will very likely clean up in several thousand years, but you see that’s not going to cut it. We need the water NOW. Biological sand filters work and if monitored they will work much more efficiently over all ( they are sustainable technology ) than anything man has yet come up with. Don’t agree with me? PROVE I’M WRONG. When those of you who are not aware of the importance of water become aware – will the amazing little microbes that so willingly eat pathogens be gone? Are you willing to risk that? Science DOES NOT KNOW EVERYTHING ABOUT THESE BENEFICIAL MICROBES, or what may eventually destroy them. Think about it folks. Happy drinking – and those of you in the city – well – enjoy your carcinogenic cocktails. Cheers! ( or you could call your local or state legislator and demand change – naaaa. . . . that makes too much sense. Sorry, but I had to say this.)

New information is available about rainwater harvesting from composition roofs. The slow sand filter described on slowsandfilter.org has been shown to remove petroleum hydrocarbons from water down to less than 1 part per ten million by weight; and this is when it is operating at its LEAST efficient rate of purification (at 32 degrees F). Also, petroleum hydrocarbons are present in roof water from the composition roof in the study in potentially harmful amounts if consumed over a long period of time (2.9 parts per million by weight). If a first flush diverter is used the, concentration is reduced to almost acceptable levels (less than 1 part per million by weight). The hydrocarbons may, in fact, be originating partially from local air pollution, because diesel fuel traces were found along with heavy oils. The implication here is that composition roofing is indeed a viable means of collecting rainwater, if proper filtering is used. A first flush diverter can be built easily with some pvc and recycled containers, and a slow sand filter can also be put together for minimal cost using recycled containers.

Another important fact uncovered is that rainwater from a roof may indeed vary WIDELY in the amount of Coliform bacteria present. The study has shown that water from a roof can contain about 60 cfu/100ml of coliform bacteria (relatively harmless) to 50,000 cfu/100ml (very likely to contain harmful pathogens and not safe to use), and that a slow sand filter will vary somewhat in its ability to remove pathogens; and also that a first flush diverter will remove a considerable number of the pathogens, but not enough to be safe. The slow sand filter has been shown repeatedly, by other studies (see the lit cited page on the above mentioned website) to remove coliform, ecoli, and fecal coliform to a safe level – from none detectable, in the best case, to 10 cfu/100ml in the worst case. In all cases the water from the filter is very non-turbid and should work well in conjunction with a UV filter
followed by an epa approved point of use tap water filter.

A small biological sand filter (slow sand filter or Biosand filter) is maintained or cleaned by actively managing only the top 5 cm of sand. This top layer is either removed and replaced when the flow rate becomes unacceptable (typically 4 to 6 months) with clean sand or “wet harrowed” meaning the sand is gently agitated causing partial break up of the biological surface. This may be slightly different for a very large slow sand filter; more sand and more work.

A rapid sand filter is maintained and cleaned by forcefully injecting water backwards through the entire sand bed every 2 or 3 days. Backwashing a biological sand filter will destroy it and may result in people getting very sick if water from it is being consumed. A Frequently asked questions (FAQ) on biological sand filters can be found here.

The terminology used to describe water filters that uttilize sand and gravel to filter water can be confusing. A “slow sand filter” uses sand and biological methods to purify water. A “rapid sand filter” uses sand to filter water. Rapid sand filters do not make use of biological methods, although some biological action may take place between backwashing (cleaning). A “Biosand filter” is a modified slow sand filter, invented by Dr. David Manz. A Biosand filter uses biological and sand filtering and is designed to operate intermittantly. A “sand filter” is a general term used to refer to a water filter that uses sand as the filter media.

Effective rapid sand filtration requires that chemicals and coagulants be added to the water. The coagulants attract particles including some bacteria. When the water with these coagulated pieces flows through sand, the coagualted particles are physically blocked by the sand. The water that emerges must be treated with chemicals such as chlorine, or ozone because most of the harmful bacteria, viruses and protozoa are still in the water. A rapid sand filter fills up in several days and must be cleaned by “backwashing” – forcing air and water back through the sand with high pressure. This breaks loose the coagulated contaminants. The resulting muck must then be drained off and disposed of. This material is hazardous waste. The bacteria is not killed, it is contained. When the chlorine or ozone is added to the water from a rapid sand filter the water  is sterilized but not purified. Sterilized means the pathogens are inactivated, but their remains are still in the water. Purified means the pathogens are removed from the water.

A slow sand filter, and a Biosand filter work much differently than rapid sand filters. To explain this it is helpful to think about biology class. To purify means to remove, to sterilize means to inactivate. From a biological standpoint, rapid sand filter systems sterilize water, biosand filters and slow sand filters purify water. All water, with the exception of distilled water, will have organisms in it. Because of this, when water passes through sand due to only the force of gravity, these organisms, that live in oxygen rich water (most water has some dissolved oxygen), will cling to the sand particles and start to feed on other organisms. In about 3 to 4 weeks a living layer of organisms forms in the top 5cm of sand. This layer continues to grow and will eventually spread throughout the filter with most of the activity concentrated in the top 5 to 10 cm of sand. Harmful organisms are “eaten” by this biological layer, which is often called the “Schmutzdecke” which is German for “dirt cover”. This results in purification. Eventually the layer on top gets so concentrated that it slows down the flow of water. To restore the flow of water, this biological layer must be “moderated” to allow more water to pass through at a higher rate. This is done in one of two ways. Either the top 2 cm of sand can be removed, or the surface can be “wet harrowed”. “Wet harrowing” means gently disturbing the biological layer and then allowing the resulting cloudy water to drain off. This is not backwashing. The lower layers of sand and organisms remain un-disturbed. Aside from biology, there are physical properties of a slow sand filter. As water and gravity act on the sand, a compaction and settling occur, which results in the sand becoming a “filter cake” which increases the effectiveness of the physical filtering properties of the system. Backwashing a slow sand filter will destroy this property and disrupt the biological action in the lower areas of the filter – in other words backwashing a slow sand filter or a biosand filter from the bottom of the filter will destroy it.  Perhaps the confusion on this method comes from the fact that some large slow sand filters use a form of backwashing to effectively wet harrow the filter. Water is forced through the top 20 centimeters ( 8 inches ) of the 4 foot deep sand bed to break loose the top layer of biological activity. The bottom 3 feet 4 inches is left completely undisturbed. This is not the same as what is used on a rapid sand filter. In a rapid sand filter the entire sand bed is forcefully disrupted regularly every 2 or 3 days. There is a huge difference here. Constructing a small slow sand filter, in a 5 gallon bucket or a 55 gallon barrel and then backwashing it by forcing water backwards through the sand from the bottom up, to clean it, is just plain stupid. If the water from this situation is being used for consumption, people will most certainly get very sick.

First; my humble apologies for being so slow to moderate comments. Vast improvement is in order. We have updated the software that runs the blog ( as of July 24 2009) which went perfectly. Moderating should be quicker now.

The slow sand filter works using biological processes. Water passes through a layer of sand and after about 3 weeks a layer of biological activity forms in the upper 2 to 3 centimeters of the sand. The bacteria in this layer sometimes called the “schmutzdecke” break down harmful bacteria such as “beaver fever cysts”, all coliform including the most deadly and the resulting water out of the filter is safe. A lively discussion about these filters would be very encouraging. Anyone who has comments, questions, or experience with these filters is encouraged to leave comments. The website http://www.shared-source-initiative.com/biosand_filter/biosand.html documents a year and a half of experience building and operating 2 of these filters built from mostly recycled materials. All tests so far have shown they work very well. Also the website http://www.slowsandfilter.org has more detailed information and an FAQ page.