Manned missions to the moon, Mars, and deep space are currently a top priority for NASA. However, the lack of technology capable of maintaining and monitoring a life support system for long-term spaceflight presents many significant challenges. Moreover, recent issues with potable water quality on-board the International Space Station (ISS) have underscored the need to develop techniques for monitoring water quality in flight. This dissertation focuses on the development and microgravity validation of colorimetric-solid phase extraction (C-SPE) technology for the in-flight monitoring of spacecraft water quality. C-SPE measures the change in the diffuse reflectance of indicator disks following exposure to a water sample. A typical C-SPE analysis can be performed in ∼2 min and requires only small, easy-to-use, lightweight hardware.;Specifically, this dissertation describes the development of C-SPE methods for determining formaldehyde and total silver. Formaldehyde is a contaminant that has recently been detected in the drinking water supplies on-board NASA spacecraft, while silver is currently used as a biocide to prevent microbial contamination of the ISS potable water supply. The formaldehyde method, which represents the first application of C-SPE to the detection of an organic analyte, can quantify formaldehyde concentrations from 0.08 to 20 ppm in ∼3 min using only ∼1 mL of sample. The total silver method builds on a C-SPE technique for detecting silver(I) that was previously developed in our laboratory. The new method determines the total concentration of silver (i.e., dissolved and colloidal) in the range of 0.1-1 ppm, which spans the ISS potable water target level of 0.3-0.5 ppm. This method also requires only ∼1 mL of water and can be completed in less than 3 min.;Included in the dissertation are the results of recent microgravity evaluations of C-SPE techniques on-board NASA's C-9 microgravity simulator. These experiments established effective methods for accurately collecting water samples of a target volume in microgravity, which had previously proven very problematic. Importantly, the flight results validated the performance of our C-SPE analyses for silver(I) and iodine (I2) under reduced gravity conditions, paving the way for a six-month technology demonstration project, scheduled on ISS for mid-2009.