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Isotopic reconnaissance of urban water supply system dynamics

Abstract. Public water supply systems (PWSS) are critical infrastructure
that is vulnerable to contamination and physical disruption. Exploring
susceptibility of PWSS to such perturbations requires detailed knowledge of
supply system structure and operation. The physical structure of the
distribution system (i.e., pipeline connections) and basic information on
sources are documented for most industrialized metropolises. Yet, most
information on PWSS function comes from hydrodynamic models that are seldom
validated using observational data. In developing regions, the issue may be
exasperated as information regarding the physical structure of the PWSS may
be incorrect, incomplete, undocumented, or difficult to obtain in many
cities. Here, we present a novel application of stable isotopes in water
(SIW) to quantify the contribution of different water sources, identify
static and dynamic regions (e.g., regions supplied chiefly by one
source vs. those experiencing active mixing between multiple sources), and
reconstruct basic flow patterns in a large and complex PWSS. Our analysis,
based on a Bayesian mixing model framework, uses basic information on the SIW
and production volumes of sources but requires no information on pipeline
connections in the system. Our work highlights the ability of stable isotopes
in water to analyze PWSS and document aspects of supply system structure and
operation that can otherwise be challenging to observe. This method could
allow water managers to document spatiotemporal variation in flow patterns
within PWSS, validate hydrodynamic model results, track pathways of
contaminant propagation, optimize water supply operation, and help monitor
and enforce water rights.
