Water is always at risk of accidental or intentional pollution that would consist of introducing a harmful chemical into a drinking water reservoir. Fiber-optics evanescent wave sensing has been shown to be an efficient sensor scheme for direct in-water sensing. Here we demonstrate a system for the detection of chemicals dissolved in water by using quantum cascade lasers (QCLs) coupled into a silver halide fiber. The study was performed over two frequency ranges: short wavelength (i.e. 3µm and 5µm) and long wavelength (between 8µm and 10µm) and using two different types of QCL source: pulsed and continuous wave.