This paper explores dairy farmers and science-policy ‘ways of knowing’ water quality. Based on case-study research undertaken in the Manawatu-Wanganui region, different ways of knowing water quality were evident. Some farmers believed more emphasis was placed upon science-policy ways of knowing above farmers’ ways of knowing. This belief contributed to farmers’ disregarding and disbelieving Horizons’ information and contributed to the strong farmer resistance to Horizons One Plan. This paper poses the question: how can multiple ways of knowing water quality be acknowledged so stakeholders can communicate and participate more effectively in policy making processes?