Carolyn Balk
Trailblazer Foundation
Siem Reap, Cambodia
All of the time I have spent sifting sand, sifting gravel, washing sand, and washing gravel has paid off! On Friday, I went to Lolei Village outside of Siem Reap to install eight water filters which–let me tell you, reader–was a very long and arduous day.
The village had no electricity, only one generator in one of the nicer houses. There was one dirt road that went through the village, houses lining either side, and a few small shops. Behind the houses were either more houses or gardens / farms / open land. Most of the villagers were at home to receive the filters, and from what I observed at least, about half of the children went to school.
We installed eight filters, which took a total of about six and a half hours including lunch, installation time, and driving time. The filter mold comes from a Canadian organization called CAWST (The Centre for Affordable Water and Sanitation Technology) that creates a lot of filter molds, I am told, for NGOs all over developing countries. The filters are immensely heavy, as they are made out of concrete, and so are the bags of sand (I really never realized how heavy sand could be). The filters are relatively easy to install seeing as they are just plopped on the ground wherever the family wants them (and this means they can be near a toilet or sewage source, but because the filter does not draw on this water (necessarily) this is theoretically fine). We installed the filters either next to their well or next to their kitchen area.
Basically, we wheeled the filter on a dolly to where the family wanted it installed. The family pays 13,000Riel, or $3.25, for the filter that then goes to the village fund. The price in 2012 was $2.60, but due to inflation, I am told, the price increased. This place has to be level in order to function properly, and in a few cases we had to add sand or a pebble or two underneath the filter in order to ensure this. We then put some water into the filter, pour the large gravel into the bottom, and level it. I leveled the gravel as I can reach the bottom of the filter with my rather long arms and still not get my sleeve wet. Then, we pour in the small pebbles, level these again, and then the sand which two people need to pick up to dump in due to its immense weight. We level the sand carefully without packing it in, and also then clean the filter using water and a cap-full of bleach. Finally, we pour more water into the filter and place the blue perforated filter contraption on top of this sand and water (it fits nicely into the concrete filter). You pour water on top of the blue filter and then, after about two weeks of being installed, clean water comes out of the drinking end.
The two-week waiting period is for the biofilm to develop and mature in the sand. The biofilm is created in the sand to trap bacteria in the water (it will consume bacteria such as E.Coli), and is developed organically and biologically specific to that water source. A biofilm for pond water would be different from a biofilm for well water, for example. The biofilm traps about 40% of the bacteria, while 60% or so of the other objects / not-so-great minerals in water (if there is a lot of iron, for example) is physically trapped with the blue filter or does not make it through the sand at all. For example, pond water had a lot of silt that is physically blocked with the sand and/or blue filter. Biosand filters trap about mid 80s to high 90s % of the bacteria and objects found in water, with percentages varying due to maintenance and quality of the original water source. When the biofilm develops after about two weeks, clean water is good to go.
The cleaner the water is going into the filter, the cleaner the water is coming out. Therefore, if you use water from a stream that feces run into, the water that comes out of the filter will not be as clean as water coming from a well 30 meters or so from a toilet. With each filter Trailblazer installs, they also hand out and explain a blue booklet in Khmer with pictures to show how to maintain the filter, how to use the filter, and how to drink/use water responsibly and sustainably in general. The pictures show fenced in livestock so they do not poo in streams, and also enclosed toilet areas, for example.
By the end of the day sand was sticking to me and my shirt nearly transparent in the back. We arrived back in Siem Reap by four, and I took a well-needed shower.