Anat Bernstein - The Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sde Boker Campus 8499000, Israel.
OrcID,Raz Studny  - The Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sde Boker Campus 8499000, Israel.
Vinolia Shyntychea  - The Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sde Boker Campus 8499000, Israel.
Yoram Katz - Mekorot, Water Company Ltd., Tel Aviv 6713402, Israel.
Berhane Abrha Asfaw  - Institute of Applied Geosciences, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
Kaori Sakaguchi-Söder - Institute of Applied Geosciences, Technische Universität Darmstadt, 64287 Darmstadt, Germany; Institute IWAR, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
OrcID,Christoph Schüth - Institute of Applied Geosciences, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
Hagar Siebner  - The Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sde Boker Campus 8499000, Israel

Trihalomethanes (THMs) are toxic disinfection by-products, formed in the reaction of chlorine with organic matter. This work aimed to study THM formation during a unique case study of managed aquifer recharge (MAR) with chlorinated desalinated seawater. THM formation was tested in the field, along a 3.0 m deep vadose zone gallery. Two small-scale experiments were conducted in the site, with untreated and with bromide spiked desalinated seawater. These were accompanied by a large-scale, ~1-month long operational MAR event. In the small-scale experiments, THM concentrations were shown to increase with bromide concentrations, with increasing dominance of the brominated species. Nevertheless, concentrations remained within the single µg/L range, which is an order of magnitude lower than drinking water regulations. Such low THM concentrations were also determined in the large-scale event. In both cases, THM formation occurred in the ponding water, without significant formation or degradation in the upper 3.0 m of the vadose zone. This study shows that MAR with chlorinated (<0.5 mg/L) desalinated seawater through sandy infiltration basins does not pose a threat to drinking water quality at this site.