To meet drinking water regulations, rather than investing in costly treatment plant operations, managers can look for ways to improve source water quality; this requires understanding watershed sources and fates of constituents of concern. Trihalomethanes (THMs) are one of the major classes of regulated disinfection byproducts, formed when a specific fraction of the organic carbon pool—referred to as THM precursors—reacts with chorine and/or bromine during treatment. Understanding the source, fate, timing and duration of the organic compounds that react to form THMs will allow identification of targeted and effective management actions. In this study we evaluated THM precursor contributions from multiple land use categories and hydrologic contexts, including novel data for urban land uses that demonstrate strong potential to release water with high THM formation potential (THMFP; median 618 μg L⁻¹): greater than storm runoff integrated across a mixed-use (1/3 natural, 2/3 agricultural) watershed (median 460 μg L⁻¹), irrigation runoff from agricultural systems (357 μg L⁻¹), or runoff from a natural forested (median 123 μg L⁻¹) and shrubland/grassland (median 259 μg L⁻¹) watersheds. While individual storm events released high THM precursor concentrations over short periods, dry season agricultural irrigation as well as urban landscapes have the potential to release water high in THM precursors for several months. Experimental bioassays and sampling along 333 miles of the California Aqueduct confirmed bioavailability and photooxidation potential of less than 10% for THM precursors, suggesting that rivers with residence times of days to weeks may act as THM precursor conduits, shuttling THM precursors from hundreds of miles away to drinking water intakes with minimal degradation. This finding has considerable implications for water managers, who may therefore consider THM precursor management strategies that target even sources located far upstream.

为了满足饮用水法规，管理人员可以寻找改善自来水水质的方法，而不是对昂贵的污水处理厂进行投资。这就需要了解关注的组成部分的分水岭来源和命运。三卤甲烷（THM）是受控消毒副产物的主要类别之一，当处理过程中有机碳库的特定部分（称为THM前体）与氯和/或溴反应时会形成三卤甲烷。了解形成THM的有机化合物的来源，命运，时间和持续时间，将有助于确定有针对性的有效管理措施。在这项研究中，我们评估了来自多种土地用途类别和水文环境的THM前体贡献，^-1）：大于混合用途（1/3自然，2/3农业）流域（中位数460μgL ^-1），农业系统的灌溉径流（357μgL ^-1）或径流的总降雨流量来自天然林（中位数123μgL ^-1）和灌木丛/草地（中位数259μgL ^-1）分水岭。虽然个别风暴事件在短期内释放出高浓度的THM前体，但干旱季节的农业灌溉以及城市景观都有可能在几个月内释放出高THM前体中的水。沿着加利福尼亚渡槽333英里进行的实验性生物测定和采样证实，THM前体的生物利用度和光氧化潜能低于10％，这表明停留时间为数天至数周的河流可能充当THM前体的管道，使THM前体在数百英里外穿梭。饮水量最少的饮用水。这一发现对水管理者具有重要意义，他们可能因此考虑甚至针对上游水源的THM前体管理策略。