Identifying (subsurface) anthropogenic heat sources that influence temperature in the drinking water distribution system

Abstract

The water temperature in the drinking water distribution system and at the customers’ taps approaches the surrounding soil temperature at ca. 1 meter depth. Water temperature is an important determinant of water quality, since it influences physical, chemical and biological processes, such as absorption of chemicals, microbial growth and chlorine decay. In the Netherlands drinking water is distributed without additional residual disinfectant and the temperature of drinking water at the customers’ tap is not allowed to exceed 25 oC. Routine water quality samples at the tap in urban areas have shown locations with relatively high soil temperatures compared to the expected modelled soil temperatures, which indicate so called ‘underground hot-spots’. In the last decades, the urban sub-surface is getting more occupied with various types of sub-surface infrastructures and some of these can be heat sources. A few recent studies tackle the anthropogenic sources and their influence on the underground, at coarse spatial scales. Little is known about the urban shallow underground heat profile on small spatial scales, of the order of 10 m × 10 m. Our research focuses on developing a method to identify and to localise potential underground hot-spots at −1.0 m at a small spatial scale. In this article we describe a method to find anthropogenic heat sources that influence temperature in the drinking water distribution system through a combination of mapping urban anthropogenic heat sources, modelling the soil temperature and extensive measurements in Rotterdam.