One type of household water treatment product that I’ve encountered here is the Biosand Filter (BSF). It was developed by Dr. David Manz of the University of Calgary nearly 20 years ago, and it is the primary technology promoted by the Center for Affordable Water and Sanitation Technology (CAWST, http://www.cawst.org). It is a modified slow-sand filter, which means it has two mechanisms to treat the water. The first is a layer of micro-organisms that live in 2 inches of stagnant water right above the surface of the sand. These micro-organisms prey on the micro-organisms that are in each batch of untreated water that is poured into the top. The second mechanism is the sand itself – the grains of sand are small enough to trap many of the remaining micro-organisms, and deplete them of the oxygen they need to stay alive since the layer is so densely packed. Water passes through the layers of sand and comes out a spout (see the diagram below; courtesy CAWST). The BSF is not perfect, and its designers do not guarantee that the water coming out the “clean” end is completely pathogen-free. Instead, they claim that it can remove 97% of bacteria and about 90% of viruses. It can not remove chemicals (but there is not a high degree of chemical pollution in rural areas like Mityana).
Fred (the aforementioned director of the chicken project) is a very busy guy – he’s implementing the BSFs in Mityana through the support of a local NGO called Connect Africa. Fred was trained by a retired American named Tex, who lives in Kampala, swears by the filters, constructs them in his backyard, and has one in his own home. In the last year, Fred has distributed 30 of them, free of charge, to schools (including Maranatha), health clinics, churches, and hotels (see the picture below, where Fred helped install 2 filters at the Good Shepherd home for physically handicapped, homeless, and orphaned children in Kampala). This isn’t exactly at the “household” level yet, but Fred hopes to get there soon. During installation, he teaches people about proper sanitation techniques, and he is on-call to receive any service and maintenance requests as they arise. So far, the requests have been very few. CAWST claims that some filters have been in operation in the field without any trouble for over 10 years. Fred recently completed his first follow-up survey with the users of the filter throughout Mityana and the results were overwhelmingly positive in every regard. The only complaint is that the filter can only provide 80 liters of improved water per day, according to Fred’s recommendations of use.
A couple of University of North Carolina studies (the first in Dominican Republic in 2005 and the second in Cambodia in 2007) showed that these filters reduced incidence of diarrhea (often the easiest outcome that can be tracked in regard to effectiveness of sanitation interventions) by 40%. I will issue a disclaimer that I have not evaluated the rigor of these studies, but if they are to be believed and the results applied universally (which is not a small leap of faith), that makes the BSF as effective as any other intervention, including chlorine (according to the 2002 WHO study mentioned in the last post). That may surprise some people, but assuming we take the leap of faith, I think it can be attributed to a number of factors. Here are a few:
- Because the water is treated at the point of use, it reduces the risk of contamination during transport.
- Even if a purification technology is lab-tested as more effective, it does not guarantee that it is more effective in its field implementation. The easier a technology is to use, the more likely it will be implemented as it is intended to be, and the BSF is about as easy as you can get. You pour water in the top, and it pushes out water that has passed through the sand layers. There’s almost no waiting, no moving parts, no energy required, and nothing for the user to do but make sure they have a clean container for the improved water (Fred trains people on this, as well).
- Even though the BSF does not filter out every pathogen, it requires no additional operating costs, so people use it every time they drink water. In contrast, household chlorination use can be intermittent depending on the variability a household’s disposable income (sometimes a head of household will forego purchasing a chlorine tablet when they are short on cash)
- There are other reasons to use the filter besides health benefits – after filtering, the water tastes better, has less sedimentation, and it cools as it passes through the sand. No other technology has these three quality improvements, and at least in Mityana, this was often stated as one of the finest attributes of the filter.
I don’t think this last point can be stressed enough. People in Mityana are not necessarily educated about health and disease, and even after education, sometimes all that information can seem removed from their normal daily activities. People may not internalize the fact that they have had less disease or illness unless they are asked about it, and may not attribute a reduction in any disease or illness to anything in particular. Others might think they don’t have the resources to implement appropriate sanitation in their home. Aesthetic benefits like the ones described above provide an instant rationale for using the BSF above and beyond the less immediate or less-easily associated health benefits. Boiled water takes a long time to cool down, and even then, it’s not really all that cool.
The BSFs are currently being rolled out in two ways across many countries. First, through a subsidized NGO approach, where the filters are provided for free like Fred has done. Second, through a micro-enterprise model where local people construct the filters themselves (the filters can be constructed entirely of locally-available materials) and sell them and provide related services in their communities.
I’m no public health specialist, so someone please drill me if I’m out of line. I’m of the opinion that the best intervention is one that works within people’s own rationale to move a step in the right (read: healthy, economically beneficial, socially beneficial) direction. I think we all need to be wary of the “something is better than nothing” mentality, because sometimes it’s not. But I think in this case, the BSF is better than nothing, especially if it means people will be introduced to sanitation and hygiene methods for the first time. What do you think? I’m happy to have someone argue with me on this one.
Of course, the best thing that people can do is use the BSF in combination with a disinfectant such as chlorine. But isn’t this a good place to start? Below is a picture of the filtered water from Tex’s house – it looked beautiful and tasted great.