Liberian Literacy Foundation

Clean drinking water for all?

At least one third of the population in

developing countries has no access to

safe drinking water. The lack of adequate

water supply and sanitation facilities causes

a serious health hazard and exposes many

to the risk of water-borne diseases: There

are about 4 billion cases of diarrhea per

year, out of which 2.5 million cases end in

death, mostly among children under the age

of five. This is equivalent to one child dying

every 15 seconds or 20 jumbo jets crashing

every day. Solar Water Disinfection (SODIS)

can contribute to improve this precarious

situation.

What is SODIS?

Solar water disinfection is a water treatment method:

• to improve the microbiological quality of drinking water

• using solar UV-A radiation and temperature to inactivate

pathogens causing diarrhoea

• used at household level under the responsibility of the

individual user

• that is simple in application

• that relies on locally available resources, plastic bottles, and

sunlight, a renewable energy source

• that is replicable with very low investment costs

How does SODIS work?

SODIS, Solar water disinfection is a simple method to

improve the quality of drinking water by using sunlight to

inactivate pathogens causing diarrhea. Contaminated

water is filled into transparent plastic bottles and

exposed to the full sunlight for 6 hours. During the

exposure, the UV-A radiation (wavelength 320-400nm) of

the sunlight destroys the pathogens. A synergy of UV-A

and temperature occurs, if the water temperature rises

above 45°C.

Limitations of SODIS

• SODIS does not change the chemical water quality

• SODIS does not increase the water quantity or reduce

water shortages

• SODIS requires relatively clear water (turbidity less

than 30 NTU)

• SODIS is not useful to treat large volumes of water

• SODIS requires suitable climate and weather

conditions. Regions well suited for SODIS are located

between latitude 35°N and 35°S

exposure time:

 6 hours under bright or up to 50% cloudy sky

 2 consecutive day under 100% cloudy sky

 During days of continuous rainfall, SODIS does not perform satisfactorily.

Water boiling or rainwater harvesting is recommended during these days.