The role of water security in sustainable development and in the nexus of water, food, energy and climate interactions is examined from the starting point of the definition of water security offered by Grey and Sadoff. Much about the notion of security has to do with the presumption of scarcity in the resources required to meet human needs. The treatment of scarcity in mainstream economics is in turn examined, therefore, in relation to how each of us as individuals reconciles means with ends, a procedure at the core of the idea of sustainable development. According to the Grey-Sadoff definition, attaining water security amounts to achieving basic, single-sector water development as a precursor of more general, self-sustaining, multi-sectoral development. This is consistent with the way in which water is treated as “first among equals”, i.e. privileged, in thinking about what is key in achieving security around the nexus of water, food, energy and climate. Cities, of course, are locations where demands for these multiple resource-energy flows are increasingly being generated. The paper discusses two important facets of security, i.e., diversity of access to resources and services (such as sanitation) and resilience in the behavior of coupled human-built-natural systems. Eight quasi-operational principles, by which to gauge nexus security with respect to city buildings and infrastructure, are developed.

We examine the opportunities and challenges of deploying integrated organic Rankine cycle (ORC) engines to recover heat from low-temperature jacket-water cooling circuits of small-scale gas-fired internal combustion engines (ICEs), for the supply of combined heat and power (CHP) to supermarkets. Based on data for commercially-available ICE and ORC engines, a techno-economic model is developed and applied to simulate system performance in real buildings. Under current market trends and for the specific (low-temperature) ICE + ORC CHP configuration investigated here, results show that the ICE determines most economic savings, while the ORC engine does not significantly impact the integrated CHP system performance. The ORC engines have long payback times (4–9 years) in this application, because: (1) they do not displace high-value electricity, as the value of exporting electricity to the grid is low, and (2) it is more profitable to use the heat from the ICEs for space heating rather than for electricity conversion. Commercial ORC engines are most viable (payback ≈ 4 years) in buildings with high electrical demands and low heat-to-power ratios. The influence of factors such as the ORC engine efficiency, capital cost and energy prices is also evaluated, highlighting performance gaps and identifying promising areas for future research.