Household Water Treatment and safe Storage (HWTS) systems aim to provide safe drinking water in an affordable manner to
users where safe piped water supply is either not feasible or not reliable. In this study the effectiveness, economic
parameters and costs of three selected HWTS systems were identified. The selected systems are SODIS, ceramic filter and
biosand filter. These options were selected based on their accessibility, affordability and available scientific data.
Data was obtained through peer-reviewed literature, reports, web-pages and informal sources. The findings show a wide
dispersion for log removal of effectiveness of the HWTS systems. For bacteria (
In many parts of the world, people do not have access to safe drinking water, this is especially true in rural areas of developing countries (Unicef et al., 2012). Conventional piped water delivery and similar centralized systems are not feasible for rural and peri-urban communities in the near future, implying that they are left with the responsibility (and need) to collect, treat and store their own water (Brown Sobsey and Loomis, 2008). Where groundwater is inaccessible or contaminated, these users depend on household water treatment (HWTS) systems for safe drinking water (Sobsey et al., 2008). These HWTS systems have the goal to provide safe drinking water in an affordable and sustainable manner (Duke et al., 2006) while being simple and easy to manage by their users (Heinsbroek and Peters, 2014). As such, these systems are crucial in reducing occurrence of diarrheal and other debilitating illnesses (Meierhofer and Landolt, 2009; Stauber et al., 2009). Efficiency in providing safe water differs per method. To indicate removal efficiency, the WHO produced guidelines (WHO, 2004) to define default performance targets to indicate a certain removal efficiency for different pathogens as “interim”, “protective” or “highly protective” (see Fig. 1).
WHO guidelines on default performance targets of HWTS systems (WHO, 2004).
When looking at the economics of HWTS systems, it is common practise to look
at the price per produced m
Schematic illustration of SODIS.
SODIS is based on the principle of disinfection by solar radiation (see Fig. 2). The procedure is straightforward; an unscratched and uncoloured PET or glass bottle is filled with water and exposed to direct sunlight for a minimum of 6 h (Heinsbroek and Peters, 2014). Water with low oxygen and high turbidity levels has to be pre-treated (Acra et al., 1990; Meierhofer and Landolt, 2009).
The ceramic filter is based on the following principle: a porous media of fired clay that retains microbes by size exclusion and high tortuous properties (it traps microbes in the sharp bends; Hunter, 2009; Sobsey et al., 2008; van der Laan et al., 2014). Many variations of ceramic filters exist; e.g. pot filters or “water purifier” (see Fig. 3; Akvopedia, 2014b; Potters for Peace, 2014a), candle filters (Sobsey et al., 2008) and Tulip siphon filter (Basic Water Needs, 2014; Tulipfilter, 2013). Periodic scrubbing and rinsing is necessary to remove impurities (Sobsey et al., 2008).
Schematic illustration of ceramic Pot filter (Van Halem et al., 2007).
Biosand filters consist of a concrete or plastic frame filled with crushed rock (sand) filter media of 0.15–0.35 mm particle (Murphy et al., 2010b; see Fig. 4). Two filter mechanisms govern the removal principle of biosand filters: physical removal of organic matter and turbidity (Sobsey et al., 2008) and biological removal of colloidal particles and harmful pathogens in the so-called Schmutzdeke (Duke et al., 2006; Hunter, 2009; Weber-Shirk and Dick, 1997). The filter can be cleaned manually by removing the top few centimetres of sand and disposing the overlying water (Sobsey et al., 2008).
Schematic illustration of biosand filter (not on scale).
In this section an in-depth description is given of the removal mechanisms of each of the selected HWTS systems and the corresponding removal efficiency. Both lab and field studies are used to give an overview of the reported effectiveness. Insufficient data was found on the log removal of protozoa, so this pathogen is excluded from this study.
The inactivation mechanisms of the solar radiation is based on direct UVB
absorption (damaging the pathogenic DNA), optical inactivation (via reactive
oxygen species) and thermal inactivation (denaturation; Reed, 2004). A
synergy between optical inactivation and thermal inactivation was signalled
at temperatures between 40–50
Log removal of SODIS for bacteria.
Log removal of SODIS for viruses.
In Figs. 5 and 6, a summary is given of the found removal efficiencies
of SODIS for bacteria (
By means of meta-regression, Hunter (2009) concluded that compared to other interventions (chlorine, SODIS, biosand filter and combined coagulant-chlorine), the ceramic filter shows the highest effectiveness on the long term. Most filters are manufactured by adding colloidal silver to increase efficiency. Silver inactivates bacteria and other pathogens through three mechanisms: reaction with thiol (in structural groups and functional proteins), structural changes in cell membrane and reaction with nucleic acids (Russell et al., 1994) . There are different ways to impregnate silver in the filter: dipping, painting, pulse injections and fire-in (Oyanedel-Craver and Smith, 2007; Ren and Smith, 2013). Van der Laan et al. (2014) and Oyanedel-Craver and Smith (2007) did not find a significant difference in removal efficiency for different silver application methods. On the contrary, the storage time in the receptacle of a silver-impregnated filter was found to be an important parameter in the bacterial removal efficiency; lengthy contact time in the receptacle led to higher removal efficiencies (van der Laan et al., 2014). Neither does an addition of iron appear to increase the removal efficiency in their research (Brown et al., 2008). Concerns exist about the virus removal of ceramic filters, since reported removal efficiencies do not reach WHO guidelines (Murphy et al., 2010a; van der Laan et al., 2014), and show high distribution (Bielefeldt et al., 2010). No critical parameter was yet identified to improve the virus removal efficiency (van der Laan et al., 2014).
Log removal of ceramic filters for bacteria.
Log removal of ceramic filters for viruses.
In Figs. 7 and 8, a summary is given of the found removal efficiencies of
ceramic filters for bacteria (
The removal mechanism of the biosand filter is based on the slow sand filtration principle and depends on the daily volume loaded to the filter (Elliott et al., 2008). The optimal volume is investigated to be equal to or smaller than the pore volume (Elliott et al., 2011). When larger charge volumes are exposed to the filter, a decrease in removal efficiency is found (Baumgartner et al., 2007). Although this HWTS system is designed for intermitted use, continuous use of the biosand filter has higher removal efficiencies (Young-Rojanschi and Madramootoo, 2014). Introduction of iron oxide in the sand layer shows improved levels of pathogen removal and is especially beneficial after cleaning or in the ripening period (Ahammed and Davra, 2011). It is suggested that the Schmutzdeke contributes to the virus attenuation by the production of microbial exo-products (proteolytic enzymes) or grazing bacteria on viruses (Elliott et al., 2011; Huisman et al., 1974). Concerns exist about the lack of guidelines for the post-treatment of the removed Schmutzdeke during maintenance since this contains opportunistic pathogens and therefore poses an health risk to consumers (Hwang et al., 2014).
Log removal of biosand filters for bacteria.
Log removal of biosand filters for viruses.
Figures 9 and 10 provide a summary of the reported removal efficiencies of
biosand filters. Overall, the reported log removals of biosand filters for
bacteria (
Figures 5–10 show that the removal efficiency of HWTS systems differs per pathogen type and per study. The removal efficiencies found in the reviewed articles, are not always compatible with the target performance of the WHO (see Fig. 1), which corresponds with the results of previous studies such as Murphy et al. (2010a) and van der Laan et al. (2014). The difference between highest and lowest reported efficiencies of each HWTS system is what makes the difference between safe or unsafe water produced with this particular HWTS system. Hence, the question arises whether certain removal efficiency can be guaranteed for the HWTS systems.
Overview of the overall range of found log removals in Sects. 2.1–2.3 for bacteria.
Overview of the overall range of found log removals in Sects. 2.1–2.3 for viruses.
In Figs. 11 and 12, the total range of lowest to highest reported log removal reported is shown per HWTS system. It can be seen that SODIS have the highest reported efficiency for bacteria removal (9 log removal) whereas, biosand filter report the highest reported efficiency for virus removal (7 log removal). Biosand filters show the lowest (zero) removal efficiency for bacteria whereas for virus removal, all HWTS systems have been reported with a zero log removal in one or more studies.
In the past, numerous studies questioned the effectiveness of HWTS systems. Various field test results indicated that HWTS systems may not always improve and sometimes even worsen the pathogenic state of the water (Murphy et al., 2010a). The lack of blinding and considerable heterogeneity in the results of HWTS systems show signs of concerns (Hunter, 2009). Moreover, it is reported that the research method can have a big impact on the reported efficiency (van der Laan et al., 2014). The reported removal efficiency also depends on the indicator pathogen used, as shown by Palmateer (1999) and Elliott et al. (2008). Quality tests are not yet globally standardized (Rayner et al., 2013), so that a fair comparison between data sets is challenging.
Operating conditions can also reduce the effectiveness of HWTS systems (Baumgartner et al., 2007). The effectiveness of HWTS systems does not only depend on technology, but also on human factors. When the HWTS system is not operated properly, exposure to pathogens can remain high. For example, it is common that people use the storage container of the device to collect dirty untreated water to feed the HWTS system, reducing the effectiveness of the device (Murphy et al., 2010a). Other reasons why in practice the effectiveness of HWTS systems is reduced: (i) only part of the used water is treated (Sobsey et al., 2008), as the water production of HWTS systems can be reduced in time due to clogging (ii) replacement-purchases are unfeasible (Brown et al., 2009; Hunter, 2009; Meierhofer and Landolt, 2009), (iii) the water is only intermittently treated (Sobsey et al., 2008), (iv) limited guidance to determine whether pre-treatment is necessary (Sobsey et al., 2008), (v) usage of the device simply stopped (Hunter, 2009), or (vi) selling it to a friend or relative (Brown et al., 2009). For ceramic filters, the rate of participation reduction is estimated at 2 % per month (Brown et al., 2009). The found diversity in effectiveness prompts that sufficient training and continued monitoring is needed to increase and sustain proper HWTS device management. Preferably, this could be done by a well-embedded local agent in order to increase acceptability (Meierhofer, 2006). Understanding the human factors that influence the real effectiveness of the HWTS systems is crucial for widespread adoption and sustained usage (Sobsey et al., 2008).
In this section, the parameters that determine the purchase price of a HWTS system (see Fig. 12) and the reported prices for the three selected HWTS systems are discussed (see Table 1).
Overview of the price and retail price of HWTS systems.
Economic Parameters that determine the costs of HWTS systems.
The price of HWTS systems depends strongly on project area (Potters for Peace, 2014b; H. Jansen, personal communication, 2014). This can be explained by the fact that the price of HWTS systems is determined by (at least) four parameters (see Fig. 12). The first cost-parameter for HWTS systems is the production costs (or investment costs) including, materials (plastic, sand, ceramic), labour and basic tools (Basic Water Needs, 2014; Potters for Peace, 2014). These costs depend on the type of HWTS system and the region of production. Factories in China and India are frequently used, due to lower labour costs. The second parameter is distribution (Stuurman et al., 2010). Transport costs between production and project area depend on quantity and weight. In-land and over-sea transportation can differ considerably in total cost. For example, getting new ceramic filters to Ethiopia from India is more economic over-sea than over land (Basic Water Needs, 2014). This parameter is estimated to be the most dominant (Basic Water Needs, 2014). However, high variability in both manufacturing and transportation costs translate into a severe limitation in data regarding the relation between costs in logistics and retail price. Local production factories are established to diminish distribution costs and enhance local economy (Brown, 2007). The third parameter is taxes. Depending on the country, HWTS systems need to be imported and import fees are involved. A possible fourth parameter is the (local) distributor's fee that is required to maintain his business. A retailer (of spare parts) of HWTS systems in Ethiopia, for example, can only remain in business if earnings are sufficiently attractive (Basic Water Needs, 2014). Depending on the developed supply chain, a (local) distributor will organize or co-organize distribution and sales in the project area.
Price ranges (USD m
Only a limited number of peer-reviewed articles mention costs of HWTS
systems, and in general only retail prices were mentioned. Retail price
depends on the four parameters mentioned in the previous section and is the
price eventually paid by the user. The retail price could be converted to
the price per m
In Table 1, a summary is given of the price per m
Ranges for the retail price of the three selected HWTS systems (outlier of SODIS is neglected).
Overall, it is found that the biosand filter has the lowest price per
m
Most cost estimations of HWTS systems are found on websites of coordinating NGOs or device suppliers. Because the information is practice-oriented, the reliability of this information is likely to be fluctuating. More direct information from local producers turned out to be necessary. For example, Resource Development International in Cambodia reveals a standing quotation of a ceramic filter for USD 12 (RDI, 2014), which is in line with the prices in other sources. Since the price of HWTS systems does not only depend on the four parameters mentioned before, but is also fluctuating in time and susceptible to exchange rates. The price of the HWTS system today is therefore different from the price indicated for 2007 (PRACTICA Foundation, 2014). This study does not include these changes. The prices mentioned in table1 are considered to be valid for the year of the respective reference.
In this study the removal efficiencies and economics of three selected Household Water Treatment and safe Storage (HWTS) systems were compared: SODIS, ceramic filters and biosand filters. Overall, no direct relationship between HWTS system's removal efficiency and economics was observed. This article aimed to be a guide through the currently available HWTS, however, it may be concluded that insufficient reliable information is available for a straightforward recommendation for the most effective and affordable HWTS.
For SODIS, low retail prices and intermediate prices per m
The authors would like to thank Jens Groot (Basic Water Needs), Herman Jansen (PRACTICA Foundation), Sreymeh Chan (RDI), Kaira Wagoner (Potters for Peace) and Laura Schuelert (CAWST) for their contribution to this research. Edited by: Luuk Rietveld