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

Abstract

Abstract. The water temperature in the drinking water distribution system and at customers' taps approaches the surrounding soil temperature at a depth of 1 m. Water temperature is an important determinant of water quality. In the Netherlands drinking water is distributed without additional residual disinfectant and the temperature of drinking water at customers' taps is not allowed to exceed 25 • C. In recent decades, the urban (sub)surface has been getting more occupied by various types of infrastructures, and some of these can be heat sources. Only recently have the anthropogenic sources and their influence on the underground been studied on 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. Routine water quality samples at the tap in urban areas have shown up locations -so-called hotspots -in the city, with relatively high soil temperatures -up to 7 • C warmer -compared to the soil temperatures in the surrounding rural areas. Yet the sources and the locations of these hotspots have not been identified. It is expected that with climate change during a warm summer the soil temperature in the hotspots can be above 25 • C. The objective of this paper is to find a method to identify heat sources and urban characteristics that locally influence the soil temperature. The proposed method combines mapping of urban anthropogenic heat sources, retrospective modelling of the soil temperature, analysis of water temperature measurements at the tap, and extensive soil temperature measurements. This approach provided insight into the typical range of the variation of the urban soil temperature, and it is a first step to identifying areas with potential underground heat stress towards thermal underground management in cities.

Drinking Water Temperature around the Globe: Understanding, Policies, Challenges and Opportunities

“…Measurements of soil temperatures in The Netherlands have shown that soil temperatures at depth of 1.0 m in a warmer than average summer with a heat wave can reach very local up to 27 • C and can heat up at a rate of 1 • C per day, in so-called 'hot-spot' locations. Examples of 'hot-spot' locations are industrial areas with large anthropogenic heat sources, with no vegetation and good drainage that prevents infiltration and fully exposed to the sun radiation [21].…”

“…Although several soil temperature models for rural areas have been proposed, little is known about the soil temperature profile in urban areas. A one-dimensional soil temperature model was developed by Blokker and Pieterse-Quirijns [11] and extended by Agudelo-Vera et al [21] to include anthropogenic heat sources, as seen in Figure 5. Drinking water temperature in tropical countries could be even higher; nine water samples collected on different days in the city of Cali (Colombia) resulted in temperatures between 25 °C and 28 °C [24].…”

“…Drinking water temperature can significantly increase or decrease during distribution from the source to the customer. This change is strongly influenced by the weather, the depth of installation of transport and distribution pipes, the soil type, ground water levels, presence of anthropogenic heat sources and hydraulic residence times [11,21]. At the building level, drinking water temperature can also be affected by the layout of the hot water installations [14].…”

“…In the urban environment, temperatures easily approach the 25 • C limit during a warmer than average summer. Locally, under the influence of anthropogenic heat sources such as district heating pipes or electric cables, the temperature in the DWDS can temporally and locally be higher than 25 • C [21]. Yet, there remains a paucity of information regarding drinking water temperature in the DWDS, especially in countries where temperature limits are not enforced.…”

“…Measured temperature versus the calculated water mean age along flow routes for a network with two Service Reservoirs (SRs), with permission from the American Society of Civil Engineers (ASCE)[19].Water 2019, 11, x FOR PEER REVIEW 9 of Schematic representation of the one-dimensional soil temperature model, with permission from Copernicus Publications[21].…”