This thesis is concerned with the detection of low energy beta emitting radioisotopes from a source of groundwater, with particular emphasis on tritium (³H). This is investigated firstly through an understanding of the challenges of detecting tritiated water, which involves the use of Monte Carlo simulations, numerical analysis and the development of simple scintillator-based detector system. Secondly, by a novel exploration of heterogeneous scintillators, utilising scintillator fabrication, Geant4 simulations and a refined detector prototype. And finally, by the design and testing of a flow cell detector based on the novel heterogeneous scintillator, including the detection of transient tritium concentration levels. The results have demonstrated that the beta particle in the tritiated water undergoes attenuation which causes a shift in the detected energy spectrum, which is particularly relevant for single crystal scintillator detectors used to discriminate radioisotopes by comparing beta spectra. The heterogeneous scintillator used was fabricated through a granulation method, before being used to validate simulations resulting in a novel heterogeneous scintillator configuration. The results of the flow cell and associated detection showed tentative validation of the theory, showing how a short detection time would impact on detector performance.