Catchment management versus capital-intensive approaches to drinking water quality compliance: evidence from a cost-effectiveness analysis

Catchment management approaches to improving drinking water quality have become a popular alternative to costly water treatment which deals with the consequences of water quality issues rather than tackling them at source. These schemes have the potential to enhance water quality and deliver multiple additional benefits including carbon sequestration, biodiversity, erosion/flood defence, greater amenity value contributing to health and well-being, and benefits to the local economy. However, more evidence is needed to demonstrate their cost-effectiveness. This paper reports on a cost-effectiveness analysis of catchment-based vs capital-intensive approaches to achieving drinking water compliance in the pesticide MCPA and THMs (trihalomethanes) in the Derg catchment on the Ireland/Northern Ireland border. The analysis identified a hybrid strategy as the best solution combining capital-intensive and catchment management approaches. There was insufficient evidence that THM breaches could be prevented with catchment measures so capital measures would be required. However, the study found that, projected over a 30-year period, the estimated cost of MCPA compliance was £12.1M using capital-intensive approaches, whereas catchment approaches could be more cost effective by a factor of three at £3.4M, though this depends critically on the underlying assumptions such as the farmer uptake of glyphosate and its approval status.Costs of achieving drinking water quality compliance via capital-intensive vs catchment-management approaches are compared in a cost-effectiveness analysisThere is insufficient evidence that THM compliance is achievable through catchment managementIn the case of MCPA compliance, catchment approaches could be more cost-effective by a factor of three, though this depends critically on the underlying assumptionsBehavioural change takes time and catchment management must be sustained over the long term to compete effectively with capital-intensive solutionsBy providing evidence of the potential water treatment cost savings through catchment measures, this study makes a case for catchment management in certain situations