Slow sand filter update

It is now January 27 of 2017. Its been cold this past 6 weeks: below freezing for 42 days with only 5 days where the temperature was in the upper 30s during the daytime. The ground remained frozen the entire 42 days. That’s 42 nights of  below freezing temps here, mostly in the lower 20’s. All of the filters, with the exception of filter 3, and 4,  were frozen solid until 5 days ago. Filter 3 and 4 froze up when I forgot to increase the flow at night. Had I kept the flow up they would not have frozen. Filter 3, and 4 are the ones that have continuous flow 24/7 from the use of a small pump that either recirculates water through them or runs water through them from a surface well. When I am able I will check all the filters out to determine the extent of damage, if any, and i will post it here. Most of the pipes were not glued, so they just pushed apart with no damage, but I will need to check more closely as the weather warms up. This has happened before just about every year and the filters just keep on working. This year the cold spell lasted slightly longer.

Posted in slow sand water filter study and construction | 2 Comments

How long will a slow sand filter last ?

How long will a slow sand filter “run” before it needs “repair”?

This is a good question. This blog has 8 years of posts documenting the slow sand filters running here. I can say with certainty that the longest running filter here (filter 1) is still fully functional after 8 years of continuous running (with the exception of several weeks each winter when all the filters freeze up and stop running). In filter 1, the sand has not been changed and the filter has not been wet-harrowed; and no sand has been removed or added. Recirculation is used in the summer when little or no rainfall occurs.

The other filters running here have been in continuous service for various lengths of time. Anywhere from 5 years to 8 years. All filters, with the exception of the 5 gallon filters, and the smaller 1/2 gallon filter, are still fully functional and currently in service. The 5 gallon filters were not successful, and we have stopped working with them. The smaller 1/2 gallon filter was never fully tested thoroughly enough to show any success.

Posted in slow sand water filter study and construction | 4 Comments

Rain water harvesting in Washington DC

According to one of our contributors, Kristan,  it is legal and encouraged in The District of Columbia to harvest rainwater. (see the most recent comment at the bottom of this page on our blog) They have extensive information on how to manage storm water in the District of Columbia. The link below offers some interesting reading.

Read more about this here.

Posted in slow sand water filter study and construction | Leave a comment

Colorado legalizes rain water harvesting

The governor of Colorado has signed into law a bill that allows anyone to collect rainwater from their roof. It is now legal to collect rainwater in Colorado. 

HB 16-1005 is the bill that was signed May 12, 2016.  

More here:

And here:

This is a big change from the past one hundred and fifty years or so. It has been a crime in Colorado set up a rain water harvesting barrel until May 12, 2016. Now it is legal. The times, they are a changin’.

Now I am sure there will be people ranting about something they find bad about this. There will be nit-pickers that will find, and point out, limitations and regulations. No matter, this is still a huge positive change brought about by hard work from everyone involved. Change can and does happen, but it takes a long, long time.

Thanks to Susan, for bringing this to my attention.

Posted in slow sand water filter study and construction | Leave a comment

Water molecules have now been shown to have a fourth “state of matter”

A recent article in “Science World Report” explains how scientists have found a new property of water molecules. A close examination of this information may give new clues as to how a slow sand water filter actually works on the molecular level.  It has been found that water molecules act differently when in microscopically confined spaces such as those which occur in natural environments:

“According to the researchers, such confinements, which are usually 5 angstroms across, are fairly common in nature and occur in environments such as cell walls, mineral interfaces, and dirt.”

In these confined spaces water molecules do not act specifically like solid, liquid or gas.  This may be of interest when determining how slow sand water filters are able to remove some types of petrol chemical contaminants from water, such as PAHs, and THMs.

Hopefully, this above link will remain active for longer than a few days.

Posted in slow sand water filter study and construction | Leave a comment

An update on rain water harvesting in Colorado

Colorado appears to be coming around regarding their laws on rain water harvesting.  Its about time given the results of this study which shows that residential home owners catching rain in 55 gallon barrels does not adversely effect the amount of water that makes it to the subsurface. Actually, catching rain water may actually increase the amount of water that makes it to the subsurface; by preventing evaporation. Water caught in a rain barrel is meant to be used – that is – returned to the ground; not hoarded to never be seen again. It looks like Colorado lawmakers finally have come to their senses?

Posted in slow sand water filter study and construction | 1 Comment

Urban runoff kills salmon

Update July 18, 2016: Please refer to the comment below by Nat. There is a link to the original study.

Here is a very good reason to set up rain barrels, and slow sand filters. Urban runoff is killing salmon.  It has been known for a long time that urban runoff contains lots of nasty stuff. Common sense tells us that just about anything can be in rain water once it hits the ground. Petroleum, weed killers, herbicides, drugs, chemicals, fertilizers, and anything that people use outdoors will wash off impervious surfaces and will be in urban runoff. That water then runs to the nearest drain and from there right into rivers, creeks, streams, lakes and oceans. If every house had a rain barrel at each downspout, urban runoff during heavy rain events would be reduced, and the water could slowly filter through the soil.  Add to that a slow sand filter, and the water would be cleaned up even more. The article states:

“scientists have mentioned a relatively easy fix that is the filtration through a simple, soil-based system.”

A simple soil based system is essentially a slow sand water filter. We’ve been shouting this out for the past 7 years: slow sand filters clean up water nicely. Others have been saying the same thing.

A copy of the study can be found here

Another article about the same thing is here.



Update October 11, 2015:

Today this article showed up suggesting that 55 gallon barrels filled with, gravel, soil, and compost cleans up the water:

Update October 27, 2015 The link above is no good. 

Here is another link to the same article, captured by another site.

Update February 2016: the above two links are now dead. I cannot find the information they had written. I guess information about urban runoff  poisoning salmon is not very important to some people.


“However regardless of the perpetrator is, the researchers have already got an answer—filter runoff via a fifty five-gallon drum barrel stuffed with gravel, soil, and compost, and the fish survive.” In this quote the author, David Bryan, must mean “regardless of who the perpetrator is”.  The article goes on to state:

“After researchers filtered the water by a 3-foot-excessive soil column containing gravel, sand, compost and bark layers, all the coho survived in addition to they did in clear water.  Exams confirmed the filtration columns lowered heavy metals by fifty eight p.c and polyaromatic hydrocarbons, that are byproducts of gasoline combustion, by ninety four %.”


Update February 19, 2016:  Here is another link to a similar article  regarding urban runoff and salmon; hopefully this one won’t disappear in a few weeks.


I think the author means Polycyclic aromatic hydrocarbons, although they are also referred to as polyaromatic hydrocarbons, but they are most commonly called PAH’s. We tested for hydrocarbons in January of 2010 nearly 6 years ago in one of our slow sand filters. A slow sand filter takes out hydrocarbons. The filter we tested isn’t even 3 feet deep, and it still took out hydrocarbons and harmful bacteria.  Here is another site with information on slow sand filters, (the biosand filter is essentially a slow sand filter with a slightly different design and name, the same principle of operation is used).  There is another site here. Both of these sites have been around longer than ours, and they have plenty of information about slow sand filtration. In fact, this technology has been around for over 100 years. Read about it here.

This is serious stuff. Really! Its just not making national news. This runoff kills salmon in hours. We are continuously allowing toxic water to pollute everywhere. We remove forests, and replace them with blacktop and other types of impervious surfaces, shopping malls, and houses without any thought of the consequences. Now we’re all paying for it. In our neighborhood here,  its not uncommon to see people out in the street at the edge of their front yards with a can spraying the “weeds”. The next week its all brown dead stuff there. Then it rains and all that crap, mixed with tire dust, PAH’s, and oil, runs right down into bear creek, which then runs into Lake Washington. These people should think about it the next time they want a drink of water, or go to that fancy restaurant and order salmon.

Posted in slow sand water filter study and construction | 5 Comments

Regarding water, do trees make a difference?

This study, published in 2008, explains how trees in boreal forests help to form clouds. Boreal forests are found in the northern hemisphere. Pine trees, larch trees, and other conifers make up the majority of types of trees found in boreal forests. These trees give off “turpenes” that help to form clouds. Clouds often make rain, and can reflect heat away from the earth. Since rain is essential for rain water harvesting, and we get lots of our water from rain, it might be a good idea to have as many trees around as possible.

Posted in slow sand water filter study and construction | Leave a comment

Think about water

An update regarding our ongoing work on slow sand filters. All of the filters here are still working. The oldest, filter 1, is working after 8 continuous years running. Filters 2, 3, 4, and 5 are still working.

Here in Washington state, it has been a hot dry summer, and the fall is starting out dry also. If we get a repeat of last winter’s lack of snowfall retention in the Cascade mountains, there will be major concerns regarding water here in western Washington state.

On another similar topic; the Earth’s ground water is being used up faster than it is being replaced. In areas where there are large aquifers that are used to supply water, this is a huge problem.

It might be a good idea for people to learn about biological sand filtration and rain water harvesting sooner, rather than later. Think about water.  There’s lots of info in this blog about slow sand filtration and rain water harvesting.

Posted in slow sand water filter study and construction | 1 Comment

Cryptosporidium in swimming pools

A recent news article has warned of cryptosporidium parasites in pool water.  Another article warns of the same problem. These microbes cannot be removed or killed effectively by the use of chlorine. Ozone is effective but requires high concentrations of the chemical to kill cryptosporidium and the system must be designed specifically for that purpose.

There is an alternative that neither of these articles mentions. Slow sand filtration is the most effective way to actually remove cryptosporiduim from water.

From the EPA site on page 19:

“Of the technologies available to the drinking water industry, membrane processes (forms of micro- and ultra-filtration) appear to provide the most significant levels of Cryptosporidium removal. Conventional treatment practices appear capable of meeting 2-log removals in most of the cases studied to date. Although direct filtration and in-line filtration may be expected to be less effective than conventional treatment, this has not yet been demonstrated in a conclusive manner. Alternative technologies such as diatomaceous earth filtration and slow sand filtration appear capable of achieving comparable, if not better, levels of Cryptosporidium removal than conventional treatment. A comparison of removal efficiencies of some bench-, pilot-, and full-scale water treatment processes is presented in Table 3 below.”

Slow sand filters do not use  chemicals to filter water. They use naturally occurring beneficial non-toxic bacteria that actually eat cryptosporidium microbes and all other dangerous micobes. A slow sand filter is actually a small wetland that purifies water naturally. These filters are inexpensive and require very little maintenance and no added chemicals. They are totally sustainable. This entire blog is about slow sand filtration.  Why aren’t these people using them?

More about cryptosporidium removal here.

and here.

and here (see page 2 of the document) greater than 99.9 percent removal (removal not just killing – ozone or chlorine only kill the microbe)

Posted in slow sand water filter study and construction | Leave a comment