Reducing consumer demand is part of a multidimensional strategy to increase water resilience. Theory-based ‘nudges’ or behaviour-change strategies may be effective at reducing demand at little cost. This paper reports a unique partnership between GlaxoSmithKline, water utility Anglian Water, and researchers at the University of East Anglia. Two experimental studies drawing on the strengths of these organizations investigated a behaviour change intervention designed to reduce water usage when toothbrushing. Study 1 tested the efficacy of three theory-based behavioural messages (social norms, ingroup norms, and collective efficacy) designed to encourage participants (N = 164) to turn off the tap whilst brushing teeth. In an actual toothbrushing scenario, all three messages proved to be effective compared to a no-treatment control condition. In study 2, homes in Newmarket, Suffolk (N = 382) were given toothbrushing packs containing a collective efficacy message that highlighted turning off the tap while toothbrushing. Smart-meter recorded water usage was obtained for three weeks before and three weeks after receiving the toothbrushing packs. Household water usage significantly decreased after receiving the packs. A control group of N = 382 households did not show a significant decrease in water usage during this timeframe. These studies suggest that behavioural messages from public or private companies can be effective in reducing real-world water usage while toothbrushing. This model of collaboration between industry, water utilities, and academics can serve as a model of best practice for public and private companies interested in reducing household water usage