In November, 2013, Herbal Medics sent a core team of four volunteers to the clinic in San Juan de Nicaragua, located in the southeast corner of the country. Herbal Medics had coordinated with the director of this clinic (Dr. Sandoval) several months prior to this trip as the clinic had extensive need for clean water. Due to inadequate septic field management, most of the ground water in this town of approximately 2000 inhabitants is contaminated.
This Herbal Medics team used two 55 gallon, food-grade barrels, sand, gravel and charcoal to construct a system that fit into the existing water tower and well pump system used by the clinic. All materials were gathered locally. The sand and gravel were pre-cleaned and strained and filtered using relatively clean river water from a more remote upriver location.
The filtration system runs 24 hours a day and is gravity fed from a top (pre-existing) cistern. The filtration barrels have a combined drip rate of approximately 8 gallons per hour, and fill a post-filtration cistern that holds about 250 gallons. Clinic usage was estimated at a maximum of 150 gallons per day. The slow sand filtration exceeds that usage by about 34 gallons per day and has a float valve in the filter input.
The concept of slow sand filtration was explained to representatives of the clinic as they observed the process of the filters being built and installed. Once a filter cake layer has formed (a bacterial layer at the top of the sand that takes approximately 21 days to form), the water will achieve 99% filtration. of pathogens. Even prior to this filter cake formation, however, this system is a highly successful filtration method. Herbal Medics teams added a final charcoal tube (2″ PVC) to the filter in order to filter chemicals and improve flavor.
The clinic is now using this filter exclusively for their water source and it is the only purified water in the village.