Environmental monitoring of fresh surface waters is essential to protect human and animal health and ensure compliance with regulation. There are ongoing challenges around where and when to monitor water quality in order to meet these requirements, take advantage of new sensor technology and balance complex budgetary constraints. In this work, statistical modelling tools based on generalised additive models, functional data analysis and multivariate methods enabled interrogation of historical monitoring data and the ability to assess the capability of current and future monitoring network designs to provide evidence on water quality trends. Evidence from such statistical and data analytic approaches enabled assessment of compliance with water quality monitoring regulation and informed the design planning for monitoring networks, with a view to improving water quality monitoring within practical and budget constraints.