Household Water Treatment and Safe Storage Factsheet: Source ...

Household Water Treatment and Safe Storage
Fact Sheet: Solar Disinfection (SODIS) Key Data
Inlet Water Criteria
Turbidity < 30 NTU (Nephelometric Turbidity Units)
Treatment Efficiency
Laboratory
Bacteria Viruses Protozoa Helminths Turbidity Chemicals
99.9-
99.99% 0 90-99.9%0 90-99.99% 3 > 100% 3 0% 0%
Field 91.3-99.4% 0 Not available Not available Not available 0% 0%
1 Wegelin et al (1994)
2 Saladin (2002)
3 Dependent on reaching a water temperature of 50°C
SODIS can reduce the potential viability of Cryptosporidum parvum oocysts, although longer
exposure periods appear to be required than those established for bacteria (Méndez-Hermida
et al., 2007; Gómez-Couso et al., 2009). SODIS alone should not be expected to inactivate all
Cryptosporidum parvum oocysts.
Operating Criteria
Flow Rate Batch Volume Daily Water Supply
1-2 litres/bottle per
6-48 hours
1-2 litres/bottle Dependent on the number of bottles and weather
Use a transparent, non-coloured plastic bottle made from polyethylene terephthalate (PET)
Do not use plastic bottles made from polyvinyl chloride (PVC) since it contains additives that
may leach into the water
Some types of glass bottles (i.e. those with a higher content of iron oxide, like window glass)
should not be used since they do not transmit as much UV-A light
Bottles should be filled to ¾ of their capacity, capped and shaken for 20 seconds, and then
filled to the top
Requires 6 hours in full sun or up to 50% cloudy sky; or 2 consecutive days for more than
50% cloudy sky
Placing bottles on surfaces that reflect sunlight increases the treatment efficiency
Treated water should be kept in the same bottle until it is consumed
Robustness
Bottle can be used as a safe storage container
Requires suitable climate and weather conditions; most favourable location: between
latitudes 15° and 35° north/south; next most favourable location: between latitudes 15°
north/south and the equator
PET bottles are abundant in urban areas, but may be less so in rural areas
Not useful for treating large volumes of water, several bottles needed for a large family
Bottles will soften and deform if the temperature reaches 65°C
Users are unable to determine by their senses when sufficient disinfection has taken place,
and so need to keep track of them to know which bottles have been treated and ensure that
they always have treated water
Estimated Lifespan
Bottles become scratched or aged by sunlight and must be replaced periodically