Based on the full article “Revolutionizing water security in rural Chile: The potential of a rainwater harvesting treatment system” by MSc Sarah Wind
Introduction
The Ñuble region, central southern Chile, receives high winter precipitations, but unfortunately the degraded soil and watershed conditions, mainly caused by the monoculture forestry sector, is unable to hold on to this water for the dry summer months. Water shortages are thus a seasonal challenge, and many residents rely on trucked-in water supplies (Frêne et al., 2014). The increasing costs and localities in water stress have heightened the interest in rainwater harvesting to locally save rainwater from the abundant winter precipitation, providing a self-sufficient and cost-effective water source. (Infante & Infante, 2013).
Rainwater might seem pure, but its quality can vary significantly. As it falls through the atmosphere, rain collects various contaminants (De Buyck et al., 2021). The composition of the rainwater is influenced by nearby human activities and natural events, such as industries, traffic and agricultural practices, and sea spray, forest fires and volcanic activity (Sánchez et al., 2015). Roof-harvested rainwater can also be contaminated by the roofing material itself, gutters, and plumbing components (Barriga et al., 2024). Finally, rainwater is deficient in minerals like calcium and magnesium, which are essential for human nutrition(Naser et al., 2020). To make rainwater suitable for drinking, a comprehensive treatment process is necessary.
A rainwater harvesting and storage system (RHSS) generally consists of a catchment, storage and distribution area, and a treatment system. The treatment system may consist of several components such as diverters, filters, membranes or sterilization equipment (Jordan et al., 2008). A rainwater treatment system is necessary to ensure that the quality of the water at the point-of-use (POU) remains within the national and international Drinking Water Quality Standards (DWQS). Moreover, an efficient treatment system depends on a clear understanding of the contaminant types and concentrations present in the rainwater.
Based on a literature review of both water quality (contaminants and deficiencies) and treatment options, I’ve designed and implemented a rainwater treatment system for a homestead in rural southern Chile. The goals of the treatments are to remove all harmful contaminant concentrations, mineralize the rainwater with essential minerals like calcium and magnesium, affordability and availability, while minimizing water loss.
Contaminants and mineral deficiency
My literature research led to the following list of contaminants that are presumably present in the rainwater I harvest (Barriga et al., 2024; Cereceda-Balic et al., 2012; Cousins et al., 2022; De Buyck et al., 2021; Gómez et al., 2021; Gwenzi et al., 2015; Hamilton et al., 2019; Sánchez et al., 2015):
· Trace metals: Arsenic, Cadmium, Lead, Molybdenum, and Zinc
· Aromatic carbons: Benzene and Benzo[a]pyrene
· Pesticides: MCPP, Malathion, Glyphosate, Fenitrothion, Methoxychlor, Atra-, Sima-, and Propazine
· Emerging contaminants: PFAS
· Microbial contamination: Bacteria and pathogens
Finally, rainwater is deficient of certain minerals that are essential for human nutrition (Nihlgård, 2001). Water loses its minerals primarily during the evaporation stage of the water cycle. When water from oceans, lakes, and rivers evaporates, it leaves behind dissolved minerals. Finally, as opposed to ground- and surface water, rainwater does not contact mineral-rich soil and rocks (Hossen et al., 2023). Calcium and magnesium are the most important minerals considering their significant impact on water quality and human health. Although the content of calcium and magnesium can be obtained by a variety of foods, drinking mineralized water complements a healthy diet (Naser et al., 2020). Moreover, humans tend to absorb minerals from water more easily than minerals from food (Cotruvo & Bartram, 2009). Nevertheless, no DWQS exists about the minimum level of minerals (Naser et al., 2020).
Treatments in the rainwater harvesting system
The treatment system includes several components, each targeting specific water quality issues (see table and illustration below):
Illustration 1. RHSS with treatment system by Sarah Viento. Grey pipes are sanitary and blue pipes are pvc.
Table 1. Rainwater treatment components. Numbers according to their installation sequence; from rainwater deposition to point-of-use. After treatment 1-8 the water is used for washing and cooking. After treatment 8 water for showering is disinfected by a heat treatment (60 degrees Celsius). After treatment 9-10 the water is used for drinking.
No. | Component | Material | Comments | Treatment | Treatment mechanism |
1 | Roof (steep) | Galvanized zinc | Roof: 98m2, covering a surface area of 36m2. | Reduction of trace metals, PAHs, pesticides, and emerging contaminants. | Smooth and steep catchment area reduce settlement of contaminants |
2 | Gutters | Galvanized zinc | |||
3 | Strainer | Mesh | Screen over downspout | Large organic matter filtering | |
4 | First flush | Synthetic | 10 liters (0.1-2.5 mm of rain) | Diversion of first rainwater | |
5 | Tanks | Synthetic | 2 x 5400L | - | |
6 | 50 microns filter | Mesh | Washable, protects water pump | Organic matter filtering | |
7 | 5 microns filter | Paper | Washable, replacement after 6 months | Fine organic matter filtering | |
8
| Activated carbon block filter
| Activated carbon in block form and polypropylene (PP) screen | Replacement after 6 months | Reduction of trace metals, PAHs, pesticides, and emerging contaminants | Contaminant absorption |
9 | Mineral filter | Maifan or medical stone | Refillable cartridge | Remineralization | Mineral release |
10
| UV filter | UV sterilization lamp | Placed near to point-of-use | Bacteria and pathogens | Sterilization |
Please note that the efficiency of any filter depends on water pressure, water flow, contact time, and perhaps more water system characteristics. Also, make sure to change filters and/or perform maintenance timely. Specifications of individual RHSS can be compared with the technical information of the filters or inquiries can be made at the hardware store.
Sediment Filtration (3, 4, 6, 7, 8)
A first flush diverter and sediment filters were installed to remove large debris and particles that accumulate on the roof (Gwenzi et al., 2015; Jordan et al., 2008; Sánchez et al., 2015; Zhu et al., 2004).
Activated Carbon Filter (8)
To address organic pollutants, pesticides, trace metals and emerging contaminants a granular activated carbon block filter was used. Activated carbon is known for its high adsorption capacity, effectively capturing contaminants (sources will be available in the article or upon request).
Maifan Stone (9)
A refillable filter containing Maifan stones, also known as medicinal stone, was used to re-mineralize the water. Maifan stone is rich in minerals such as calcium, magnesium, potassium, and iron (Li et al., 2022). Additionally, Maifan stone has natural adsorptive properties, meaning it can also help remove residual heavy metals and organic compounds (Guo et al., 2022; Yang et al., 2020).
UV Sterilization (10)
Following the Chilean legislation for potable water, the addition of chlorine is the only treatment permitted for disinfection. However, chlorine leaves by-products and residual chlorine in the treated water both of which may cause health problems (Luo et al., 2020; Mazhar et al., 2020). To eliminate bacteria and pathogens without chemicals, this system uses an UV light sterilizer (Bui et al., 2021; Jordan et al., 2008; Lee et al., 2017; Sánchez et al., 2015). It is advisable to install it close to the point of use for potable water to prevent the reintroduction of microbiological contaminants after sterilization.
NB: I use a hot water boiler on top of my pellet stove to heat the water for showering and frequently heat the water to over 60 degrees Celsius to ensure any harmful bacteria are eliminated. However, if you do not have this system in your home, you can place the UV filter after the carbon block to disinfect the entire home system instead.
Results and discussion
Water samples were analyzed after passing through the system. The results showed that arsenic, cadmium, molybdenum and lead were not detected in the sample. A concentration of zinc was detected, but its value remained under the thresholds of both national and international drinking water quality standards. However, the water remained deficient in essential minerals until it passed through the Maifan stone filter.
The Maifan stone proved effective not only in adding beneficial minerals, but also in slightly alkalizing the water, making it more suitable for human consumption. This was an advantage over other mineralization methods, such as calcite or magnesium filters, which either lack mineral diversity or the ability to balance the water’s pH effectively.
The water analyses of the installed rainwater harvesting system were also compared to those of the current potable water supplied by the sanitary services (APR) of the Ñuble region. The treated rainwater resulted to be of higher quality (lower concentration of harmful trace metals) based on all parameters that were analysed.
Conclusion
The study concluded that rainwater harvesting, when combined with a carefully designed treatment system, can provide safe, potable water for rural households in southern Chile. It also shows that rainwater harvesting may deliver water of higher quality than that provided by the local sanitary services.
In the future I would like to do more water analyses to have data on the exact performance of the treatments and during various times of the year. I am currently applying for funding for this purpose, and any additional help is welcome.
This blog post is based on my scientific article that I hope to publish next year. I have published this blog ahead of the publication to share my results with anyone who may find it useful. Thanks for reading and please let me know if you have any questions.
Sarah Viento
Cited works
Barriga, F., Gómez, G., Diez, M. C., Fernandez, L., & Vidal, G. (2024). Influence of Catchment Surface Material on Quality of Harvested Rainwater. Sustainability (Switzerland), 16(15). https://doi.org/10.3390/su16156586
Bui, T. T., Nguyen, D. C., Han, M., Kim, M., & Park, H. (2021). Rainwater as a source of drinking water: A resource recovery case study from Vietnam. Journal of Water Process Engineering, 39, 101740. https://doi.org/10.1016/J.JWPE.2020.101740
Cereceda-Balic, F., Palomo-Marín, M. R., Bernalte, E., Vidal, V., Christie, J., Fadic, X., Guevara, J. L., Miro, C., & Pinilla Gil, E. (2012). Impact of Santiago de Chile urban atmospheric pollution on anthropogenic trace elements enrichment in snow precipitation at Cerro Colorado, Central Andes. Atmospheric Environment, 47, 51–57. https://doi.org/10.1016/J.ATMOSENV.2011.11.045
Cotruvo, & Bartram. (2009). Calcium and Magnesium in Drinking-water.
Cousins, I. T., Johansson, J. H., Salter, M. E., Sha, B., & Scheringer, M. (2022). Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS). In Environmental Science and Technology (Vol. 56, Issue 16, pp. 11172–11179). American Chemical Society. https://doi.org/10.1021/acs.est.2c02765
De Buyck, P. J., Van Hulle, S. W. H., Dumoulin, A., & Rousseau, D. P. L. (2021). Roof runoff contamination: a review on pollutant nature, material leaching and deposition. In Reviews in Environmental Science and Biotechnology (Vol. 20, Issue 2, pp. 549–606). Springer Science and Business Media B.V. https://doi.org/10.1007/s11157-021-09567-z
Frêne, C., Ojeda, G., & Santibáñez, J. (2014). Agua en Chile: diagnósticos territoriales y propuestas para enfrentar la crisis hídrica. (Cristián Frêne CongetPedro M. Andrade Araneda, Ed.). América Ltda. www.aguaquehasdebeber.cl
Gómez, V., Torres, M., Karásková, P., Přibylová, P., Klánová, J., & Pozo, K. (2021). Occurrence of perfluoroalkyl substances (PFASs) in marine plastic litter from coastal areas of Central Chile. Marine Pollution Bulletin, 172, 112818. https://doi.org/10.1016/J.MARPOLBUL.2021.112818
Gwenzi, W., Dunjana, N., Pisa, C., Tauro, T., & Nyamadzawo, G. (2015). Water quality and public health risks associated with roof rainwater harvesting systems for potable supply: Review and perspectives. In Sustainability of Water Quality and Ecology (Vol. 6, pp. 107–118). Elsevier B.V. https://doi.org/10.1016/j.swaqe.2015.01.006
Hamilton, K., Reyneke, B., Waso, M., Clements, T., Ndlovu, T., Khan, W., DiGiovanni, K., Rakestraw, E., Montalto, F., Haas, C. N., & Ahmed, W. (2019). A global review of the microbiological quality and potential health risks associated with roof-harvested rainwater tanks. Npj Clean Water, 2(1). https://doi.org/10.1038/S41545-019-0030-5
Hossen, M. A., Salauddin, M., & Badsha, M. A. H. (2023). A Systematic Literature Review on Rainwater Quality Influenced by Atmospheric Conditions with a Focus on Bangladesh. Environmental Science and Engineering, 53–75. https://doi.org/10.1007/978-981-99-4101-8_5
Infante, A., & Infante, F. (2013). PERCEPCIONES Y ESTRATEGIAS DE LOS CAMPESINOS DEL SECANO PARA MITIGAR EL DETERIORO AMBIENTAL Y LOS EFECTOS DEL CAMBIO CLIMÁTICO EN CHILE. Agroecología, 8(1), 71–78.
Jordan, F. L., Seaman, R., Riley, J. J., & Yoklic, M. R. (2008). Effective removal of microbial contamination from harvested rainwater using a simple point of use filtration and UV-disinfection device. Urban Water Journal, 5(3), 209–218. https://doi.org/10.1080/15730620801977174
Lee, M., Kim, M., Kim, Y., & Han, M. (2017). Consideration of rainwater quality parameters for drinking purposes: A case study in rural Vietnam. Journal of Environmental Management, 200, 400–406. https://doi.org/10.1016/J.JENVMAN.2017.05.072
Luo, Y., Feng, L., Liu, Y., & Zhang, L. (2020). Disinfection by-products formation and acute toxicity variation of hospital wastewater under different disinfection processes. Separation and Purification Technology, 238, 116405. https://doi.org/10.1016/J.SEPPUR.2019.116405
Mazhar, M. A., Khan, N. A., Ahmed, S., Khan, A. H., Hussain, A., Rahisuddin, Changani, F., Yousefi, M., Ahmadi, S., & Vambol, V. (2020). Chlorination disinfection by-products in municipal drinking water – A review. Journal of Cleaner Production, 273, 123159. https://doi.org/10.1016/J.JCLEPRO.2020.123159
Naser, A. M., Rahman, M., Unicomb, L., Parvez, S. M., Islam, S., Doza, S., Khan, G. K., Ahmed, K. M., Anand, S., Luby, S. P., Shamsudduha, M., Gribble, M. O., Narayan, K. M. V., & Clasen, T. F. (2020). Associations of drinking rainwater with macro-mineral intake and cardiometabolic health: a pooled cohort analysis in Bangladesh, 2016–2019. Npj Clean Water, 3(1). https://doi.org/10.1038/s41545-020-0067-5
Nihlgård, B. (2001). Mineral Nutrients in Water: Quality Variation of Rainwater, Surface Water, and Ground Water ©. In Combined Proceedings International Plant Propagators’ Society (Vol. 51).
Sánchez, A. S., Cohim, E., & Kalid, R. A. (2015). A review on physicochemical and microbiological contamination of roof-harvested rainwater in urban areas. Sustainability of Water Quality and Ecology, 6, 119–137. https://doi.org/10.1016/J.SWAQE.2015.04.002
Zhu, K., Zhang, L., Hart, W., Liu, M., & Chen, H. (2004). Quality issues in harvested rainwater in arid and semi-arid Loess Plateau of northern China. Journal of Arid Environments, 57(4), 487–505. https://doi.org/10.1016/S0140-1963(03)00118-6
Comments