Solar Water Purification Bags
The Puralytic Solar Bag is a 3-liter version of the LED-based Shield at Water Distribution Centers. It is a flat clear plastic bag with an embedded nanotechnology mesh, a large fill port on the top and a strong reinforced ring for hanging. It uses the same photocatalytic process as the Shield, but is activated by sunlight rather than LEDs.
Along with equipment for two complete Water Distribution Centers, we plan to take 60 solar bags, some of which will be used as discretionary gifts for local officials and UN and NGO partners. The rest are intended to offset distribution difficulties, e.g, as an alternative for a family that can only afford to have one person stand in line for the daily gallon allotment at the WDC.
Solar bags work best on a bright sunny day. It takes at least three hours to purify water. On overcast days it can take four hours or more.
Depending in the weather, a bag can be used as many as three times over the course of 12 hours, which is enough fill a four-gallon jerrycan about three-fourths full.
There is no indicator for when a bag's capacity to clean water is exhausted, although 500 cycles is considered normal. As a rule of thumb, replace bags every three months (e.g., spring, summer, fall and winter).
A small bottle of blue food coloring is included with every dozen bags. If you are concerned about the effectiveness of a bag, add a single drop before sealing and placing the bag in the sun. the food-grade dye we use is a tiny molecule. It will be the last contaminant cleared. If the blue is gone, the water is safe.
• Bags must be used outside only. Windows filter out key light frequencies.
• Water must be virtually clear
• As a rule of thumb, let the bag sit in the sun from one mealtime to another (e.g., breakfast to lunch, lunch to dinner)
• Wipe the spout of solar bag with dilute bleach (5% sodium hypochlorite solution) before pouring contents into a jerrycan to avoid accidental contamination. While the water in the bag may be clean, the spout may still harbor bacteria.
• It is vitally important that whomever we give a bag to understands how to use it properly. Teaching should always be done with a local translator, one-on-one.
• Corrugated tin and light colored roofs are ideal spots to set up bags. The bags are small and easily pilfered, so look for a safe place, preferably with friendly observers nearby.