Influence of seasonal variation on water quality in tropical water distribution system: is the disease burden significant?

Abstract

Recent evidence shows that water distribution system (WDS) is a major risk factor in piped water supply system and the degree of contamination of water in WDS is usually influenced by seasonal variation. Risk assessment studies eliminate the effect of seasonality whenever annualized estimate of concentration of contaminants in water is used to determine the risk to health. In tropical climate where strong seasonal variation prevails, the excess risk during dry and hot season, above the annualized risk can be significant. This study investigates what impact seasonal adjustment may have on health improvement targets for WDS. Water quality data of two Nigerian water supply schemes were used to estimate the impact of WDS on water quality. Seasonal deviation from the annualized impact was quantified as the latent risk in disability-adjusted life years (DALYs). The hazards identified in both WDSs were cadmium and lead, and the estimated 95th-percentile risk of the metals, over the course of dry season was about 31-38%, and 1-3% higher than the estimated yearly average risk, respectively. Wilcoxon signed-rank test showed that the risk distributions during the dry season was significantly higher (p < 0.05) than the yearly average. The median latent risks (5th, 95th-percentiles), for both WDS were 0.014 (7.6 × 10(-3), 0.023) and 4.8 × 10(-3) (-, 7.6 × 10(-3)) DALYs/person/year for cadmium and 0.87 × 10(-3) (0, 0.1 × 10(-3)) and 0.16 × 10(-3) (0, 0.031 × 10(-3)) DALYs/person/year, respectively, for lead. These risks are substantially higher than the WHO limit (1 × 10(-6) DALYs/person/year). Therefore, to achieve effective health improvement target, mitigation measures should be planned and executed by season.

Intermittent Water Supply: Prevalence, Practice, and Microbial Water Quality

“…33,69 In two IWS systems in Nigeria, leaching of cadmium was higher in the dry season than the wet season and, overall, levels were higher than in studies in CWS systems, which the authors hypothesize was due to higher dry season temperatures and stagnation from intermittency. 32…”

“…In large distribution systems, intermittent delivery can be rotational, with water provided to hydraulically isolated parts of the network in sequence. − For example, in distribution systems in Hubli-Dharwad, India, and Nablus, Palestine, water is piped once every 3–4 days with rotational supply to different zones. , In contrast, small systems may supply water to an entire coverage area at the same time. Within the same distribution systems, the nature of intermittency experienced by different parts of the network can vary in space and time, with supply durations changing based on population sizes, pressures, and pipe configurations. , …”

“…Also of note, disinfection byproducts and chemicals that leach from pipes and fittings are two other important classes of contaminants with health-related concerns that have been studied in IWS systems, including a laboratory-based study of disinfection byproducts that emulated conditions of intermittent supply and a companion study that characterized total trihalomethanes (TTHM) in Nablus, Palestine. , In two IWS systems in Nigeria, leaching of cadmium was higher in the dry season than the wet season and, overall, levels were higher than in studies in CWS systems, which the authors hypothesize was due to higher dry season temperatures and stagnation from intermittency …”

Global and local health burden trade-off through the hybridisation of quantitative microbial risk assessment and life cycle assessment to aid water management

“…Several LCA methods including ReCiPe provide human health impact assessment in DALYs and QRA methods that use DALYs have been well established (Etchie et al, 2014;Katukiza et al, 2014). In this study, there was a difference in the use of DALYs between LCA and QMRA.…”

Associations between climate variables and water quality in low- and middle-income countries: A scoping review

“…This threat is reinforced from other studies that note that the risk of disease from contaminated water in a large utility in Uganda was primarily driven by contamination in distribution systems (Howard et al 2006b). Intermittent supplies, which serve about 1 billion people in LMICs are also susceptible to seasonal deterioration in water quality (Bivins et al 2017;Etchie et al 2014;Kumpel and Nelson, 2013). The implication of these findings is that management of piped water supplies in LMICs will need to substantially improve if they are to cope with the additional threats from climate change.…”