Randomised controlled trial of thermostatic mixer valves in reducing bath hot tap water temperature in families with young children in social housing

Objectives: To assess the effectiveness of thermostatic mixing valves (TMVs) in reducing bath hot tap water temperature, assess acceptability of TMVs to families and impact on bath time safety practices. Design: Pragmatic parallel arm randomised controlled trial. Setting: A social housing organisation in Glasgow, Scotland, UK. Participants: 124 families with at least one child under 5 years. Intervention: A TMV fitted by a qualified plumber and educational leaflets before and at the time of TMV fitting. Main outcome measures: Bath hot tap water temperature at 3-month and 12-month post-intervention or randomisation, acceptability, problems with TMVs and bath time safety practices. Results: Intervention arm families had a significantly lower bath hot water temperature at 3-month and 12-month follow-up than families in the control arm (3 months: intervention arm median 45.0°C, control arm median 56.0°C, difference between medians, -11.0, 95% CI -14.3 to -7.7); 12 months: intervention arm median 46.0°C, control arm median 55.0°C, difference between medians -9.0, 95% CI -11.8 to -6.2) They were significantly more likely to be happy or very happy with their bath hot water temperature (RR 1.43, 95% CI 1.05 to 1.93), significantly less likely to report the temperature as being too hot (RR 0.33, 95% CI 0.16 to 0.68) and significantly less likely to report checking the temperature of every bath (RR 0.84, 95% CI 0.73 to 0.97). Seven (15%) intervention arm families reported problems with their TMV. Conclusions: TMVs and accompanying educational leaflets are effective at reducing bath hot tap water temperatures in the short and longer term and are acceptable to families. Housing providers should consider fitting TMVs in their properties and legislators should consider mandating their use in refurbishments as well as in new builds.