Department Sanitation, Water and Solid Waste for Development

Strategies to reduce the recontamination of treated water during transport and storage

Water that is supplied at community level in hygienically critical environments commonly is subject to recontamination during transport and storage. The availability of products and approaches to reduce these recontamination risks are of high importance to assure safe water at the point of consumption, a critical indicator for achieving SDG 6.1. To provide a contribution towards this goal we are experimenting with different approaches to enhance safe storage such as secondary disinfection using UV-C LEDs in storage containers or passive low-cost system-level chlorination, and we are assessing cleaning strategies for water containers and the development of improved water transport containers.

Influence of container design & cleaning on reducing recontamination risk

Drinking water is frequently recontaminated during transport and storage when water is poured into contaminated water containers. The design of the container has an impact on water quality. Containers are often kept at ground level, making them easily accessible to children and animals, which could be a reason for water deterioration. Hence, it is important to cover containers with lids and to store them above floor level. Water often deteriorates during extraction due to contact with contaminated hands, cups, and ladles. Hands can be prevented from entering by integrating a spout for extracting water from the containers.

Containers with narrow openings impede contact with possible contamination sources and therewith reduce recontamination risk, but they also hinder systematic cleaning of the container’s inner walls. The regular use of drinking water containers without proper cleaning leads to the formation of a biofilm in the container. This biofilm harbours bacterial colonies, provides them with food for growth, protects them from disinfection, and it consumes free residual chlorine, thus increasing the risk of contaminating water that is poured into the containers.

In the this project we collaborate with the community and local NGOs in Uganda and Kenya and Zurich University of the Arts to assess the impact of residual disinfection in combination with cleaning containers with an improved design on water quality at the point of collection and at the point of consumption and we are assessing design elements, handling and acceptance of improved water containers by users.

System-level passive chlorination

Chlorinating water to provide residual disinfection is a strategy to reduce recontamination of treated water. However, individual users’ practice of chlorinating water at the household level often is inadequate and establishing the necessary level of compliance has been found to be difficult. The installation of a passive chlorinator at the point of collection could circumvent the need to establish user compliance and can potentially increase the proportion of chlorinated water provided to the consumer. Therewith the risk that contaminated water is consumed could be reduced.

In this project we are collaborating with the local communities and the NGOs Get Water Uganda, Helvetas Swiss Intercooperation in Nepal and Sandec’s Water Supply and Treatment Goup to assess:

a) the technical performance of different low-cost designs of non-electrically powered system-level chlorinators (dosing consistency, product durability, O&M requirements, water quality),

b) business model aspects (initial and recurring cost, revenue generation models involving different stakeholders, management approaches, availability of products and spare parts)

c) user perspective ( acceptability, taste perception and williness to pay for additional cost)

d) comparing the impact of system-level passive chlorination versus the promotion of household water treatment on drinking water quality at the point of consumption and on child health

Publications

Recontamination and Safe Storage

Keeping water from kiosks clean: strategies for reducing recontamination during transport and storage in Eastern Uganda

Drinking water is frequently recontaminated during transport and storage when water is poured into jerrycans. To address this issue, three strategies aiming at reducing these recontamination risks were implemented at water kiosks in Eastern Uganda. In all three strategies, water at the kiosks was chlorinated to a free residual chlorine (FRC) concentration of 2 mg/L at the tap of the kiosk. In addition, water was collected in different containers for drinking water transport: a) uncleaned jerrycans, b) cleaned jerrycans, and c) cleaned improved containers with a wide mouth and a spigot. Water quality in the containers was compared to that of a control group collecting unchlorinated water in uncleaned jerrycans. Water samples were collected at the tap of the kiosk, from the containers of 135 households after they were filled at the tap, and from the same containers in the households after 24 h of water storage. The samples were analysed for counts of E. coli, total coliforms, and FRC. Household interviews and structured observations were conducted to identify confounding variables and to assess the influence of water, sanitation, and hygiene infrastructure and practices on recontamination.
All three intervention strategies contributed to significantly lower E. coli recontamination levels after 24 h than in the control group (Median (Mdn) = 9 CFU/100 mL, Interquartile Range (IQR) = 25). Median E. coli counts and mean FRC consumption were higher in uncleaned jerrycans (Median = 1 CFU/100 mL, IQR = 6, ΔFRC = 1.8 mg/L) than in cleaned jerrycans (Median = 0 CFU/100 mL IQR = 2, ΔFRC = 1.6 mg/L) and the lowest in cleaned improved containers (Median = 0 CFU/100 mL, IQR = 0, ΔFRC = 1.2 mg/L). The FRC concentration at the tap of 2 mg/L was too low to protect water from E. coli recontamination in uncleaned jerrycans over 24 h. Cleaning the jerrycans was inconvenient due to their small openings, therefore, sand was used. The cleaning with sand reduced recontamination with E. coli but did not reduce the count of total coliforms. Improved containers with a larger opening allowed for cleaning with a brush and showed the lowest levels of recontamination for both E. coli and total coliforms. In addition to the intervention strategies, households receiving a higher number of WASH education visits within the previous year had lower recontamination levels of E. coli in stored water (OR = 0.54, p = .003).
Gärtner, N.; Germann, L.; Wanyama, K.; Ouma, H.; Meierhofer, R. (2021) Keeping water from kiosks clean: strategies for reducing recontamination during transport and storage in Eastern Uganda, Water Research X, 10, 100079 (8 pp.), doi:10.1016/j.wroa.2020.100079, Institutional Repository

Influence of container cleanliness, container disinfection with chlorine, and container handling on recontamination of water collected from a water kiosk in a Kenyan slum

The study assessed whether using clean containers that had been disinfected with chlorine at a water kiosk in the Kangemi slum in Nairobi reduced recontamination of treated water during drinking transport and storage. At the same time, the impacts of container handling and hygiene conditions at the household level on water quality changes during storage were evaluated. Data were collected during interviews with 135 households using either new, clean Maji Safi containers (MSCs) that had been disinfected with chlorine or normal uncleaned jerrycans (NJCs). Bacteriological water quality and free chlorine levels in both types of containers were measured after container filling at the kiosk and in the same containers after 24 h storage in households. The use of MSCs significantly reduced the risk of recontaminating the treated water. After water filling at the kiosk, none of the MSCs contained Escherichia coli bacteria, and 2.8% were contaminated after 24 h storage. In contrast, 6.2% of NJCs were contaminated after filling, and 15.2% after 24 h storage. Multivariate logistic regression indicated that the use of a clean water container and sufficient chlorine and the frequency of cleaning the container in the household mitigated recontamination. We suggest further investigation of water container designs that facilitate cleaning.
Meierhofer, R.; Wietlisbach, B.; Matiko, C. (2019) Influence of container cleanliness, container disinfection with chlorine, and container handling on recontamination of water collected from a water kiosk in a Kenyan slum, Journal of Water and Health, 17(2), 308-317, doi:10.2166/wh.2019.282, Institutional Repository

Does activated silver reduce recontamination risks in the reservoirs of ceramic water filters?

Efforts to provide safe water are challenged by recontamination and regrowth of pathogens in treated water during storage. This study evaluated the potential of metallic silver with a chemically etched surface to reduce recontamination risks during water storage in ceramic water filters. Batch experiments were conducted in the laboratory with water storage buckets containing three configurations of varying amounts of silver. Field trials in a rural area in Kenya assessed the effect of the same configurations in the storage buckets of locally produced ceramic pot filters without colloidal silver coating. The tests revealed that the etched silver slightly reduced microbiological recontamination risks during water storage despite the low diffusion of silver ions (<5 µg Ag/L). The effect was strongly influenced by water chemistry parameters. A statistically significant difference in the removal of E. coli (Δ Log Removal Value (LRV) = 0.6) and total coliforms (Δ LRV = 1.7) was found between households using a filter with silver in the water reservoir and those using a filter without silver. Multivariate regression of water handling factors and hygiene practices on filter performance revealed that the presence of silver in the reservoir and cleaning the filter element with a brush were associated with a better filter performance.
Meierhofer, R.; Rubli, P.; Oremo, J.; Odhiambo, A. (2019) Does activated silver reduce recontamination risks in the reservoirs of ceramic water filters?, Water, 11(5), 1108 (11 pp.), doi:10.3390/w11051108, Institutional Repository

From water source to tap of ceramic filters - factors that influence water quality between collection and consumption in rural households in Nepal

The study assessed changes in water quality between the water source and the tap of locally produced low cost ceramic water filters used by a community living in hygienically critical conditions in a remote mountainous area in Western Nepal. Data was collected from 42 rural households during two visits. The effectiveness of filter handling on its performance was assessed through microbiological analysis, structured household interviews and structured observations. Water quality decreased significantly when source water was filled into transport containers, while the use of the filters improved drinking water quality for about 40% of the households. Highly inadequate filter cleaning practices involving the use of contaminated raw water, hands (geo mean = 110 E. coli CFU/100 mL) and cleaning tools (geo mean = 80 E. coli CFU/100 mL) stained hygienic parts of the filter. The use of boiling water to disinfect the filters was significantly correlated with improved filter performance and should be further promoted. However, even disinfected filters achieved a very low average LRV for E. coli of 0.4 in the field and performed worse than during laboratory tests (LRV for E. coli of 1.5-2). Comprehensive training on adequate filter handling, as well as better filter products, are required to improve the impact of filter use.
Meierhofer, R.; Bänziger, C.; Deppeler, S.; Kunwar, B. M.; Bhatta, M. (2018) From water source to tap of ceramic filters - factors that influence water quality between collection and consumption in rural households in Nepal, International Journal of Environmental Research and Public Health, 15(11), 2439 (14 pp.), doi:10.3390/ijerph15112439, Institutional Repository

System-level passive chlorination

Assessment of low-cost, non-electrically powered chlorination devices for gravity-driven membrane water kiosks in eastern Uganda

Recontamination during transport and storage is a common challenge of water supply in low-income settings, especially if water is collected manually. Chlorination is a strategy to reduce recontamination. We assessed seven low-cost, non-electrically powered chlorination devices in gravity-driven membrane filtration (GDM) kiosks in eastern Uganda: one floater, two in-line dosers, three end-line dosers (tap-attached), and one manual dispenser. The evaluation criteria were dosing consistency, user-friendliness, ease of maintenance, local supply chain, and cost. Achieving an adequate chlorine dosage (∼2 mg/L at the tap and ≥ 0.2 mg/L after 24 h of storage in a container) was challenging. The T-chlorinator was the most promising option for GDM kiosks: it achieved correct dosage (CD, 1.5-2.5 mg/L) with a probability of 90 per cent, was easy to use and maintain, economical, and can be made from locally available materials. The other in-line option, the chlorine-dosing bucket (40 per cent CD) still needs design improvements. The end-line options AkvoTur (67 per cent CD) and AquatabsFlo® (57 per cent CD) are easy to install and operate at the tap, but can be easily damaged in the GDM set-up. The Venturi doser (52 per cent CD) did not perform satisfactorily with flow rates > 6 L/min. The chlorine dispenser (52 per cent CD) was robust and user-friendly, but can only be recommended if users comply with chlorinating the water themselves. Establishing a sustainable supply chain for chlorine products was challenging. Where solid chlorine tablets were locally rarely available, the costs of liquid chlorine options were high (27-162 per cent of the water price).
Dössegger, L.; Tournefier, A.; Germann, L.; Gärtner, N.; Huonder, T.; Etenu, C.; Wanyama, K.; Ouma, H.; Meierhofer, R. (2021) Assessment of low-cost, non-electrically powered chlorination devices for gravity-driven membrane water kiosks in eastern Uganda, Waterlines, 40(2), 92-106, doi:10.3362/1756-3488.20-00014, Institutional Repository