Rooftop rainwater harvesting by a shallow well - Impacts and potential from a field experiment in the Danube-Tisza Interfluve, Hungary

Groundwater levels have declined significantly in the last decades in many parts of the world, due to anthropogenic activities and climate change. The study focuses on the long-term potential and environmental impacts of rooftop rainwater harvesting coupled with shallow well infiltration, which is a local scale inexpensive solution that could contribute to easing water shortage. The Danube-Tisza Interfluve (Hungary) was used as a study area, where a field experiment was set up, funneling rainwater from the roof of a family house to the shallow dug well in the yard, connected to a porous unconfined aquifer. Changes in groundwater levels, as well as thermal, hydrochemical and isotopic footprints were monitored and evaluated for over 600 days to determine the quantitative and qualitative effects of this method and to identify the long-term physico-chemical impacts of infiltrated water on ambient groundwater. During the monitoring period, 60.616 m(3) of precipitation was infiltrated through the shallow well that could achieve significant water quality improvement: Mg2+, Na+, Cl-, SO42-, NO3- concentrations and TDS decreased by 35-88% after the infiltration started and a further 35-96% decrease occurred in these parameters by the end of the monitoring period. Rooftop-collected water was enriched in Zn, Sr, Cu, Mn, Ba and Al, their concentrations being 1.9-48.2 times higher, in roof runoff than in the precipitation. The monitoring of water column changes and infiltration curve analysis after precipitation events helped identifying the clogging process that decreased the hydraulic conductivity of the well bottom by one order of magnitude. The results of this research provide information on the efficiency and environmental impacts of the pilot project and contribute to the extension of the design to town level and to similar settlements in the area. Additionally, general conclusions can be drawn to promote the implementation of similar projects in porous unconfined aquifers worldwide.