Controller for use in a wet environment

A controller 20 for controlling fluid delivery in a wet environment e.g. temperature and flow of a shower, including a housing 1 defining a sealed waterproof internal volume 5, a magnet holder moveable relative to the housing, one or more magnets 3a/b fixed relative to the holder, a plurality of sensors 4a-4o, greater than the number of magnets, fixed relative to the housing and located within the sealed internal volume, the sensors suitable for detecting the relative position of the magnet(s) and outputting a signal. The magnet holder may be a rotatable annular bezel, ring or dial 2 removably attached to the housing by an annular retainer 6 with resilient biased tabs urging interlocking projections 62 into circumferential groove 11 on housing. The projections and groove act as a bearing allowing bezel rotation. Two magnets may be located close together on the bezel, the distance between magnets is less than the distance between sensors equidistantly located in a circle within the housing. The sensors may be Hall effect sensors. Also claimed is a fluid delivery system e.g. shower, included the controller.