Abstract
Decentralized tap water systems are an important drinking water source worldwide. A good quality, high-pressure continuous water supply (CWS) is always the target of any urban settlement. However, tap water in some areas are reported with deteriorated water quality even though treated well before supplying. Such deterioration of tap water quality is reported widely from areas with low water availability and in economically poor countries where water are supplied intermittently (IWS). This study focuses in identifying tap water quality in IWS and causes of water quality degradation using nitrate-nitrogen (NO3-N) as an indicator and stable isotopes of hydrogen (δD) as tracer. Nine water reservoirs and ninety municipal tap water (ten per reservoir) samples were collected during the wet (June–September) and dry (November–February) seasons in the Kathmandu Valley (KV), Nepal. Ten percent of the tap water samples exhibited higher NO3-N than those of their respective reservoirs during the wet season, while 16% exhibited higher concentrations during the dry season. Similarly, the isotopic signatures of tap water exhibited 3% and 23% higher concentrations than those of their respective reservoirs during the wet and dry seasons, respectively. Coupling analysis between NO3-N and δD demonstrates close connection of groundwater and tap water. The results indicate groundwater intrusion as the primary component in controlling tap water quality variations within the same distribution networks during IWS. Meanwhile, the obtained results also indicate probable areas of intrusion in the KV as well as usefulness of δD as a tool in the assessment of tap water systems.
Highlights
Maintaining safe drinking water for growing populations is a major global issue
Losses of 5–35% of water (Lambert et al, 2014) through ruptures in municipal tap water networks are inevitable which can reach up to 50% in low-income countries (Dudley & Stolton, 2003). These ruptures and losses have a significant effect of water leakage faced by areas with continuous water supply (CWS) (24 h) wherein the water supply is steadily under high pressure
Negative pressure developed during the intermittent water supply (IWS) creates water losses and results in contaminations due to intrusions of the groundwater through the ruptures during water transport from the reservoir to the tap
Summary
Maintaining safe drinking water for growing populations is a major global issue. In addition, anthropogenic impacts on water sources and climate change have raised serious concerns regarding drinking water resources (IPCC, 2008). Municipal tap water networks are safe, they are vulnerable to artificial (pressure loads, management, and replacement) and natural changes (underground stresses, earthquakes, disasters) that can cause dislocations and ruptures (Chandra et al, 2016; Wols et al, 2014). Losses of 5–35% of water (Lambert et al, 2014) through ruptures in municipal tap water networks are inevitable which can reach up to 50% in low-income countries (Dudley & Stolton, 2003). These ruptures and losses have a significant effect of water leakage faced by areas with continuous water supply (CWS) (24 h) wherein the water supply is steadily under high pressure. Chemical and microbiological contamination has been found to be significantly higher during IWS than during CWS (Erickson et al, 2017; Kumpel & Nelson, 2014)
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