Cities as hotspots of indirect water consumption: The case study of Hong Kong

D Vanham,B.M Gawlik,G Bidoglio

doi:10.1016/j.jhydrol.2017.12.004

Abstract

During the last years, the city of Hong Kong has made large investments to make its urban water supply system more water efficient and sustainable. As such, its municipal water abstraction – often defined as direct water use – has decreased from 355 litre per capita per day (l/cap/d) in 2005 to 326 l/cap/d in 2013. Due to its political history, Hong Kong is unique in the world in data availability on urban food consumption. It is therefore the ideal case study to show typical urban food consumption behaviour and its related indirect water use. The objective of this paper is to show the large water quantities associated with indirect water use and that the citizens of Hong Kong can additionally save much more water by looking at this indirect water use. The current average diet in Hong Kong is very different to the average Chinese diet. It is characterised by a high intake of water intensive products like animal products and sugar, leading to a food related indirect water use or water footprint (WFcons) of 4727 l/cap/d. According to recommendations from the Chinese Nutrition Society for a healthy diet, the intake of some product groups should be increased (vegetables and fruit) and of other product groups reduced (sugar, crop oils, meat and animal fats). This would result in a reduction of the WFcons of 40% to 2852 l/cap/d. Especially the reduced intake of meat (including offals) from currently 126 kg per capita per year (kg/cap/yr) to the recommended value 27 kg/cap/yrwould results in a substantial WFcons reduction. Meat consumption in Hong Kong is extremely high. A pesco-vegetarian diet would result in a reduction of 49% (to 2398 l/cap/d) and a vegetarian diet in a 53% (to 2224 l/cap/d) reduction. Hong Kong citizens can thus save a lot of water through a change in their diet. Many of the products consumed, contribute to different levels of blue water scarcity in the regions of origin Hong Kong imports from. This poses a water-related risk to food security in Hong Kong. As all diet scenarios also result in a lower blue WFcons, they decrease this risk. In order to become sustainable, (mega)cities should reduce their dependency on distant resources and ecosystems.

Highlights

Our objective is to show that – using Hong Kong as a case study – 1) indirect water use is responsible for enormous water quantities in cities and 2) water can be saved by urban dwellers by looking at their diets
The inclusion of green water is a necessity in integrated water resources management (IWRM), as argued by most authors and institutions working on IWRM (Gerten et al, 2013; Hoekstra, 2016; Hoff et al, 2014; Jalava et al, 2016, 2014; Karimi et al, 2013; Miina et al, 2016; Ran et al, 2016; Rockström et al, 2014; Schyns et al, 2015; Vanham, 2012)
Direct urban water use has decreased in many modern cities

Summary

Introduction

The extent to which urban dwellers consume resources is key on the path to a sustainable world. One of these resources is water, which is consumed in a direct and indirect way by city inhabitants (Vanham and Bidoglio, 2014). While most people are aware of their direct water consumption, they are not of their indirect water consumption. The latter is defined as the water that is required to produce the goods and services city inhabitants consume, i.e. their water footprint (Hoekstra and Mekonnen, 2012)

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