Chapter 9.10

9.10 - Water Sterilization for Farmer Health by Placing in Bottles Exposed to the Sun

Luna Gao,University of Guelph, Canada

Suggested citation for this chapter.

Gao,L (2022)Water Sterilization for Farmer Health by Placing in Bottles Exposed to the Sun, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Introduction to Solar Disinfection (SODIS)

In 2019, 785 million people across the world still lacked access to accessible drinking-water systems (WHO, 2019), leaving them reliant on unsafe water sources such as ponds, rivers, springs, and unprotected wells (Luiz et al, 2016). For families with improved water sources, there is still a risk of recontamination from unsafe storage and handling of purified water (Luiz et al, 2016). Contamination of drinking water has a significant impact on human health and disease transmission. Each year 829,000 individuals die from diarrhea due to unsafe drinking water and poor sanitation (WHO, 2019). It is estimated that 88% of diarrheal diseases can be prevented with improved water sanitation and hygiene. Additionally, water sanitation seeks to eliminate countless water-borne diseases transmitted from vector and wildlife sources (Luiz et al, 2016). Lack of clean drinking water further affects smallholder farmers in developing nations, as they often have limited access to water infrastructures when living in rural and peri-urban areas. A study by Armah et al. (2018) found that impoverished rural households were 29% less likely to have access to improved sources of drinking water and 25% less likely to have access to better sanitation facilities compared to poor urban households.

One simple, low-cost method for water sanitation is Solar Disinfection (SODIS), a method developed in 1984 that harnesses the power of solar radiation to inactivate bacteria and viruses placed in plastic (usually polyethylene terephthalate – PET) bottles (Luiz et al, 2016, Pichel, Vivar, & Fuentes, 2019). The pathogens are eliminated via optical inactivation, thermal inactivation, or a combination of both methods (Borde et al, 2016).

SODIS has been shown to eliminate 99% of bacteria in 6 hours under mostly sunny weather (Luiz et al, 2016; Joyce et al, 1996), making water safe from E. coli, Cholera, Salmonella, and Shigella dysenteriae – bacterial pathogens that cause diarrhea, vomiting, stomach pain and dehydration (CDC, 2019, 2020, 2021a, 2021b). SODIS is a viable Household Water Treatment System (HWTS), which has since been used by 5 million people to improve drinking water quality (Luiz et al, 2016). SODIS water can be used for direct consumption, making drinks (coffee, tea, juice), washing fruits & vegetables, bathing children, and making baby food for infants over 18 months of age (Robinson et al, 2016).

Equipment Required

The SODIS method is cost-efficient, low-maintenance, and easily accessible as no chemicals or electrical power sources are required (Pichel, Vivar, & Fuentes, 2019). Due to the simplicity of use and low-manual labour requirement, all members of the family – including women and children, can use SODIS (Robinson et al, 2016). The only equipment required are PET bottles, which may be reused for 6 months before replacement (Pichel, Vivar, & Fuentes, 2019). PET bottles are widely accessible in most developing nations, and can often be purchased for $0.02 - $0.20 USD in rural markets. Individuals may reuse soft-drink containers fitting the SODIS requirements.

The United States CDC (2012), suggests using plastic PET bottles 300 mL - 2.0 L in capacity. PET bottles will have a PET symbol ( ) stamped into the bottle. Other plastic bottles (polyvinyl chloride - PVC, polycarbonate-PC) are not recommended as they have not been extensively tested for SODIS use (Luiz et al, 2016). Commercial, clear glass bottles are a suitable alternative to PET bottles (Luiz et al, 2016). The bottles should be transparent, though light-blue PET bottles are permissible (Luiz et al, 2016). Any tinted bottles (brown/green colour) should not be used, as the tint will block UV radiation needed for sanitization (Luiz et al, 2016).

The WHO recommends allocating 2.5-3 L of water per person per day, with multiple bottles allocated to each family member. If possible, label bottles designated to each person to reduce microbial cross-contamination (Robinson et al, 2016).

SODIS Method (CDC, 2012; Luiz et al, 2016)

1. Wash plastic PET bottle with water & soap (if available).

2. Fill the bottle with the clearest water available.

3. Shake bottles to oxygenate.

4. Expose bottles to sunlight by placing horizontally (ideally 90º) on a roof/rack for a minimum of 6 hours in direct sunlight (recommended 1 day) or 2 days when the sky is more than 50% cloudy.

5. Store treated water in SODIS bottles before use to avoid recontamination, the water should be consumed within 1-2 days to minimize the risk of bacterial re-growth. Water can be directly consumed from the bottle or poured into clear cups.

using SODIS

SODIS is a relatively safe method to sanitize water, with studies showing that SODIS can only maintain or improve water quality (Schmid et al, 2008). In terms of chemical leaching concerns, studies have demonstrated that the SODIS method does not trigger any leaching of chemical contaminants from PET bottles, with the benefits of pathogen elimination far outweighing any possible risk of micropollutants (Schmid et al, 2008).

When using SODIS, users should take note of the following environmental factors:

• SODIS is dependent on the availability of natural sunlight and the container. Therefore, bottles should be exposed for the recommended amount of time, and only PET/glass bottles should be used (CDC, 2012)

• SODIS water should be stored for no longer than 3 days, to reduce the risk of pathogen regrowth and recontamination (Robinson et al, 2016)

• Cloudy water should be filtered before use (CDC, 2012)

• SODIS should not be used on days with heavy rainfall (Borde et al, 2016)

• SODIS should not be used in regions beyond 30º latitude North & South, as these regions may not have enough solar intensity for disinfection (Luiz et al, 2016)

• SODIS is not recommended in areas where PET bottles cannot be easily accessed

• SODIS does not protect against chemical contaminants (McGuigan et al, 1999)

Evidence on Health

The goal of SODIS is to eliminate diarrheal-causing pathogens in water used by the target population (Luiz et al, 2016). A meta-analysis of multiple studies determined an average of 44% risk reduction of diarrheal disease when water-improvement interventions were carried out (Waddington & Snilstveit, 2009). Individual studies on SODIS demonstrate a wide range of health outcomes, from having no significant risk reduction (Mausezahl et al, 2009), to showing more than 80% risk reduction for cholera in children under 5 that consumed SODIS water (Conroy et al, 2001). This variance can be due to the many transmission pathways of diarrheal disease, while SODIS can only prevent disease transmission through contaminated water (Luiz et al, 2016). Areas with fresh water may face cross-contamination from human excretion; decreased SODIS effectiveness on specific pathogens (ie. viruses); and the correct, consistent use of SODIS are all factors that affect trials that measure effectiveness (Luiz et al, 2016). Even a 5-10% total consumption of contaminated water can nullify the health benefits of consuming treated water (Luiz et al, 2016).

studies on SODIS are often carried out via randomized controlled trials, generated from self-reported data of diarrheal incidence (Luiz et al, 2016). This method of data collection has a very short recall period, meaning user data is only viable for typically 2 days before the collection. Surveys are also prone to bias from the respondent, and staff involved with promotion (Luiz et al, 2016). Future blinded studies and studies using verifiable criteria – weight gain/loss, clinical diarrheal data – are required to gain more reliable results on SODIS effectiveness.

SODIS Alternatives

Under cloudy or rainy conditions where there is not enough sunlight for SODIS, families may choose to boil water for 10 minutes to eliminate 99% of pathogens (Robinson et al, 2016). Boiling water may cost more money, energy, and resources than SODIS due to the requirement to purchase and collect gas, coal, and wood to build a fire (Robinson et al, 2016).

Other low-cost household water-treatment systems (HWTS) include straining through a fine cloth, aeration, settlement, sand filtration, charcoal filtration, ceramic filters, and chemical disinfection - using bleach, or iodine tablets (Brikké & Bredero, 2003). Boiling and SODIS are the most cost-effective methods for water treatment, though they are unsuited for disinfecting large volumes of water – in which case chlorination may be more efficient (Brikké & Bredero, 2003). The link “Complete Guide to Water Sanitation” under “Practical Links to SODIS Methodology” (below) covers these alternatives in detail

Figure 3: Summary of approved HWTS methods, note SODIS has “High” effectiveness across all “Lab Studies“ (Latagne et al, n.d.).

Of the viable HWTS, SODIS is the most cost-efficient method. In 2007, Clasen et al. estimated that the annual cost to use SODIS is $0.63/per person compared to chlorination ($0.66/person), filtration ($3.03/person), flocculation/disinfection ($4.95), or other source-based interventions ($1.88/person in Africa). Other advantages of SODIS include having no adverse effect on taste of water – unlike chemical methods, and ensuring proper storage of water after sanitation - unlike filtration methods where water may need to be transferred to another storage container (Luiz et al, 2016).

Examples of SODIS Implementation

Local education campaigns are essential for introducing SODIS methods and increasing their rate of adoption in local communities. A study in Zimbabwe found that household training programs using champions were much more effective than campaigns without champions (Mosler et al, 2013). Furthermore, communities that understood the risks of untreated water and the role of water in causing diarrhea were associated with increased adoption of SODIS (Graf et al, 2008).

SODIS can be promoted efficiently through organizations working on water sanitation – including women’s clubs, NGOs, hospitals, community development projects, education centers, and government programs (Luiz et al, 2016). Successful SODIS programs include training over 250,000 people in Nairobi, Kenya, through information distributed by the CBO Kenya Water for Health Organization (CDC, 2012). In Latin America, over 100,000 individuals were taught the the SODIS methodology with the help of local partner organizations (CDC, 2012).

Gathering and selling SODIS bottles presents a potential small business opportunity for local individuals. SODIS permissble PET plastic and glass bottles, such as soft-drink bottles can be gathered, cleaned, and sold at markets, and in regions with limited access to bottles for SODIS use.

After SODIS programs are introduced, sustained promotion & support are necessary to encourage users to continue using SODIS in the long term (Luiz et al, 2016), with social acceptance of SODIS practices being important for the longevity of sustained SODIS use (Islam et al, 2015). For information on how to plan a SODIS campaign, see page 32-51 of the “SODIS Manual” and page 33-55 of “EAWAG Manual” in the section below.

Practical Links to SODIS Methodology

• SODIS Website [1]

• SODIS Manual [2]

• CAWST Page on SODIS [3]

• SSWT [4]

• EAWAG Manual [5]

• Centers for Disease Prevention and Control (CDC) [6]

• Video on Solar Disinfection in Ethiopia – Professor Kevin McGuigan, RCSI [7]

• Skit on SODIS [8]

• Simple Guide to HWTS Methods [9]

• Complete Guide to Water Sanitation [10]

References

1. Armah, F. A., Ekumah, B., Yawson, D. O., Odoi, J. O., Afitiri, A.-R., & Nyieku, F. E. (2018). Access to improved water and sanitation in sub-Saharan Africa in a quarter century. Heliyon, 4(11), e00931. https://doi.org/10.1016/j.heliyon.2018.e00931

2. Borde, P., Elmusharaf, K., McGuigan, K. G., & Keogh, M. B. (2016). Community challenges when using large plastic bottles for Solar Energy Disinfection of Water (SODIS). BMC Public Health, 16(1), 931. https://doi.org/10.1186/s12889-016-3535-6

3. Brikké, F., Bredero, M. (2003). Linking technology choice with operation and maintenance in the context of community water supply and sanitation. World Health Organization and IRC Water and Sanitation Centre, 72-89. Retrieved from https://www.who.int/water_sanitation_health/hygiene/om/wsh9241562153.pdf

4. CDC (2012, October 8). Solar Disinfection. Retrieved from https://www.cdc.gov/safewater/solardisinfection.html

5. CDC (2019, December 12). Salmonella Symptoms. Retrieved from https://www.cdc.gov/salmonella/general/salmonella-symptoms.html

6. CDC (2020, October 2). Cholera Symptoms. Retrieved from https://www.cdc.gov/cholera/illness.html

7. CDC (2021a, February 2). E. coli Symptoms. Retrieved from https://www.cdc.gov/ecoli/ecoli-symptoms.html

8. CDC (2021b, June 29). Shigella Symptoms. Retrieved from https://www.cdc.gov/shigella/symptoms.html

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