A Critical Evaluation of the Water Supply and Stormwater Management Performance of Retrofittable Domestic Rainwater Harvesting Systems

Abstract

Rainwater harvesting systems are often used as both an alternative water source and a stormwater management tool. Many studies have focused on the water-saving potential of these systems, but research into aspects that impact stormwater retention-such as demand patterns and climate change-is lacking. This paper investigates the short-term impact of demand on both water supply and stormwater management and examines future and potential performance over a longer time scale using climate change projections. To achieve this, data was collected from domestic rainwater harvesting systems in Broadhempston, UK, and used to create a yield-after-spillage model. The validation process showed that using constant demand as opposed to monitored data had little impact on accuracy. With regards to stormwater management, it was found that monitored households did not use all the non-potable available water, and that increasing their demand for this was the most effective way of increasing retention capacity based on the modelling study completed. Installing passive or active runoff control did not markedly improve performance. Passive systems reduced the outflow to greenfield runoff for the longest time, whereas active systems increased the outflow to a level substantially above roof runoff in the 30 largest events.Research measuring the performance of these systems in the UK is limited to monitored commercial buildings [7]; few household-scale empirical studies have been performed and are limited to single homes [8,9]. Studies in the USA have examined the stormwater performance of specifically designed active release systems which were emptied automatically before storm events [10]. However, these systems were large and installed on high-demand industrial facilities and not intended for domestic use. The long-term stormwater management of domestic systems designed for water supply is unclear.Other studies have conceptualised the systems' performance through modelling either at an allotment, neighbourhood or catchment scale. Xu et al. [11] modelled the ability of three types of allotment-scale RWH systems to simultaneously deliver the dual benefits discussed above in addition to river baseflow restoration. Using a historic 11 year rainfall dataset, they defined six metrics (the efficiency and frequency of water supply, baseflow and retention) to quantify system performance. These indicators were average values and did not indicate behaviour during storm events with specific return periods, which are of interest to drainage designers.More detailed models, such as the study of a sewer catchment in Palermo by Freni and Liuzzo [12] and the catchment response framework developed by Jamali et al. [13] capture the stormwater management of RWH systems on a larger scale. Due to the size of their spatial grid, the temporal resolution of these models was often low, in the order of daily [12] or hourly [13] time steps. Campisano and Modica [14] illustrated that their mass-balance approach proved unreliable for the evaluation of water supply ...

Quantifying the performance of dual-use rainwater harvesting systems

“…A sensitivity analysis concerning household water demand is essential as it is often assumed that householders will exclusively use rainwater for their non-potable water needs when available. However, Quinn et al. (2020) showed that householders with a downstairs toilet connected to a conventional rainwater harvesting system did not use the water available to them as often as would be expected by the British Standards Institution (2013) .…”

Closing Water Cycles in the Built Environment through Nature-Based Solutions: The Contribution of Vertical Greening Systems and Green Roofs

“…For VGS, some literature demonstrates the potential of rainwater use [46,47], but detailed experimental investigation is scarce [48]. Rainwater harvesting systems have proven to be effective as partial substitutes for domestic water demand in oceanic zones [49], as well as in semi-arid climatic zones [50], but limiting factors include the unpredictability of precipitation patterns and the size of water storage systems, which may be prohibitive [14]. On the other hand, wastewater, particularly greywater, is produced daily and, hence, can provide a continuous stream of irrigation water once treated.…”

Revealing the Challenges of Smart Rainwater Harvesting for Integrated and Digital Resilience of Urban Water Infrastructure

“…As described above, smart RWH systems are characterized by their ability to automatically release stored rainwater prior to rain events based on weather forecasts. There-fore, with reference to smart RWH approaches [8][9][10][11], the following digital uncertainties could be identified:…”

“…However, detention efficiency is strongly dependent on user behavior and withdrawal quantities in relation to the detention volume. This can be a limitation especially for traditional systems, which are therefore referred to as uncontrolled RWH systems [6,11]. For example, higher withdrawal volumes empty RWH systems faster, therefore additional storage volumes can be provided for stormwater detention.…”