Water is an integral part of our society, and it is of the utmost importance that this water is clean and safe for potable use. Drinking water sources can become contaminated with halogenated organic compounds (HOCs) via improper disposal of refrigeration or air conditioning units, industrial usage, and even through the disinfection of our drinking water (chlorination). One class of these HOCs regulated by the U.S. Environmental Protection Agency (USEPA) is trihalomethanes (THMs). THMs have been found to cause adverse health effects and can even be carcinogenic, they are limited to 80 ppb in treated water by the USEPA. Currently THM concentrations are detected in treated water using expensive analytical equipment, which have high sensitivity, but lack any portability or ease-of-use. Here we show a syndiotactic polypropylene (sPP) nanoporous electrospun fiber membrane capable of visible colorimetric detection of trihalomethanes (THMs) at environmentally relevant levels (ppb-scale), without a separate preconcentration step. The developed detection method includes a two-fold preconcentration technique coupled with a colorimetric detection reaction, integrated into a single sensor device. Here, the utilization of the colorimetric Fujiwara reaction serves as the detection reaction. This long-studied reaction has a response that is normally limited to a beaker scale visible detection range on the order of 80 ppm THMs, when a separate preconcentration step is not present. The two-fold integrated preconcentration technique consists of a thermodynamic method based on the utilization of the THM: water equilibrium in the vapor phase of the system as well as a physical method using a sPP nanoporous membrane capable of concentrating THMs in a contaminated aqueous sample. The developed device has successfully lowered the portable single-step visible THM detection concentration by an order of magnitude (80 ppm 80 ppb). This sensor was also successfully applied for the determination of the total THM (t-THM) concentration in spiked and actual treated water samples, and these results correlated well with the GC/MS results of the corresponding sample, showing its real world applicability. (C) 2015 Elsevier B.V. All rights reserved.