Environmental forensics studies for nitrate source determination (NSD) have seen increased interest in recent years. However, the numerous approaches that have been suggested do not differentiate sewage and manure sources in surface waters. This differentiation is especially important as human-health risks are higher from human, than animal, faecal contamination. Therefore, human and veterinary pharmaceuticals were exploited as co-occurring sewage and manure markers. Through an understanding of pharmaceutical use, occurrence and fate, further source characterisation can also be achieved. Pharmaceutical analysis in environmental waters has traditionally been carried out using SPE LC-MS/MS. A single method was developed and validated for six sewage and four manure markers at detection limits of up to 50 pg/L. Results from a one-year monitoring programme in Irish waters confirmed the selected suite's suitability for differentiating and characterising point and diffuse sources of sewage and manure. However, LC-MS/MS is costly, time-intensive and requires large sample volumes. Therefore, the novel application of NMR and immunoassays, was explored. The use of immunoassay techniques has shown great promise in this regard. The potential for pharmaceutical entry into surface waters through alternative pathways than sewage and manure was also assessed. Data on medication use and disposal was collated following a survey of 1449 individuals. Results show that few participants dispose of unused pharmaceuticals in the sewer. Therefore, the potential for incorrect source attribution as a result of unused medication disposal is low, confirming the suitability of pharmaceuticals as chemical markers. However, available data on NSD is highly fragmented and approach-dependent.Therefore, a decision-support tool that incorporates the considerations of interest was developed using IDEF0 modelling. This tool enables decision-makers to identify the most suitable NSD approach in a specific scenario. This tool was validated through interviews with key stakeholders, through which it was confirmed that there is, indeed, currently a need for such a decision tool.