Pharmaceutical and pesticide residues in water are emerging environmental concerns due to their potential effects on aquatic ecosystems and human health. Pharmaceuticals may enter water systems through domestic wastewater, hospital discharges, and improper drug disposal, while pesticides can reach rivers and groundwater through agricultural runoff and the improper use of chemicals. Identifying these contaminants and determining their sources are essential for effective water quality management and environmental protection. Analytical Detection and Source Identification The detection of pharmaceutical and pesticide residues requires sensitive analytical techniques capable of identifying contaminants at low concentrations. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is widely used to detect pharmaceutical compounds and many pesticides, while gas chromatography–mass spectrometry (GC-MS) is suitable for analyzing volatile and semi-volatile pesticides and other organic contaminants. Beyond detection, forensic source tracking involves comparing contaminant profiles from water samples with those collected from potential sources, such as wastewater treatment plants, hospitals, agricultural areas, and industrial facilities. The distribution and concentration of specific compounds can help investigators identify likely pollution pathways and distinguish between different sources. However, source attribution requires careful interpretation because contaminants may degrade, transform, or mix during their movement through the environment. Environmental and Forensic Significance Pharmaceutical residues, including antibiotics and painkillers, may affect aquatic organisms and contribute to concerns about antimicrobial resistance. Pesticide residues can also harm non-target organisms and threaten water quality. Environmental forensic investigations help establish the presence and distribution of these substances and provide scientific evidence to support environmental monitoring and investigations into suspected illegal discharges or improper chemical disposal. Reliable results depend on representative sampling, appropriate sample preservation, validated analytical methods, and accurate documentation of the chain of custody. Chemical findings should be combined with field observations and other relevant evidence before drawing conclusions about the source of contamination or legal responsibility. Conclusion Combining advanced analytical chemistry with forensic source tracking provides an effective approach to investigating pharmaceutical and pesticide contamination in water. These methods can help identify pollution sources, improve environmental monitoring, and support evidence-based regulatory action. Strengthening laboratory capabilities and cooperation between environmental authorities and research institutions is essential for protecting water resources and public health.