Sodis project assistant You Van explains the solar water-disinfection method to students in Rovieng district.

A cquiring clean drinking water can be as simple as filling a clear plastic bottle

with contaminated water and leaving it in direct sunlight for a day.

Known as Solar Water Disinfection (Sodis), the method uses the sun's UV radiation

to kill biological pathogens - including bacteria, parasites and viruses - found

in unfiltered water. It has a 99.99 percent disinfection rate.

Representatives from the Ministries of Health, Education, and Rural Development,

as well as relevant NGOs, gathered in Phnom Penh May 3 to see the results of a one-year

Sodis pilot project carried out in Rovieng district, Preah Vihear province.

Martin Wegelin, program officer for the Swiss government's Department of Water and

Sanitation in Developing Countries, said at the workshop that around the world a

child dies from diarrhea every 15 seconds.

He said in Cambodia, where less than 15 percent of families have access to clean

water, Sodis is a cost-effective and simple option for people.

"We just want Sodis to be an option, and the government and NGOs have shown

interest," he said. "It's about education and awareness on all levels."

Project coordinator Ryan Sinclair, 31, spent the past year in Rovieng trial testing

Sodis with approximately 1,200 people in four villages, and the results were positive.

Of the 225 households that used Sodis, diarrhea rates dropped from 21 percent to

2 percent in a six-month period. Another commune of 295 households, who were not

using Sodis, was monitored for comparison; there was no change in their diarrhea

rates over the six months.

The challenge, Sinclair said, is encouraging people to continue using Sodis as a

method of water disenfection.

"People have been using UV light to disinfect for centuries," he said.

"Cambodians leave fish, bugs, peppers to roast in the sun."

The methodology and implementation are simple, Sinclair said.

Clear plastic bottles can be filled with water from a lake or well, then placed in

direct sunlight, either on the roof or on a sheet of corrugated iron for a minimum

of six hours - two days if it is cloudy. The water is then safe to drink.

"But people need a lot of support from others they respect around them who are

using [Sodis] - they need to see that it works," he explained.

Sinclair and his colleague, You Van, worked with two local women's groups and visited

schools to educate people on Sodis.

Sinclair said the message spread to other villages by itself.

"But we just hope it lasts," he said.

Other major challenges to Sodis in Cambodia are cloudy water and quality bottle supply.

The Sodis method uses the sun's UV rays to kill the biological pathogens which can cause diarrhea

The water collected should be clear, because pathogens can tuck themselves behind

particles and hide from UV rays.

Before filling up the bottle, cloudy water can be filtered using a ceramic filter

or krama, or by letting the water settle over night.

The plastic bottle type recommended for Sodis is made from PET (polyethylene terephtalate),

as opposed to PVC (polyviny-lchloride) plastic, which has a bluish tinge to it and

is less effective in transmitting UV radiation.

Sinclair explained adults need two liters of water per day and children one liter

per day, so an extended family could require up to 12 bottles daily.

Large PET bottles, however, can be difficult to obtain for those living far from

populated areas, and this is one of the greatest challenges for Sodis if it is to

become a water-disinfection alternative nationwide.

Bottles need to be in good condition; when they become too scratched and worn, the

UV radiation can be blocked. The bottles must also be in direct sunlight and not

become shaded throughout the day.

Sinclair, who drank only Sodis water during his year in Rovieng, said observers of

Sodis have aired concerns over the possibility of chemicals from the plastic contaminating

the water during its solar disinfection period. But he said risk assessments have

proven there is nothing to worry about.

Data to back up his claims was presented at the Sodis workshop, which showed no plastic

by-products, such as formaldehyde or acetaldehyde, in Sodis water. Furthermore, the

maximum concentration of carcinogenic substances was lower than World Health Organization

guidelines for drinking water.

Solar water-disinfection methods are currently used in 20 developing countries, including

Thailand, where the program has been in practice since its introduction in 1993.

Sodis is a project of Adventist Development Relief Agency (ADRA) in Cambodia and

is funded by the Swiss Federal Institute for Environmental Science and Technology.