Background: Unsafe drinking water and household air pollution are leading risk factors for diarrhoea and pneumonia, two major causes of death for young children. Rural areas are vulnerable due to unsafe water supplies and biomass burned indoors for cooking. Household water filters and portable fuel-efficient cookstoves could reduce these risks, but there is limited evidence of longterm uptake and impact. National Water Quality Study: To determine the extent of faecal contamination of household stored drinking water and associated risk factors in Rwanda, we conducted a nationally representative cross-sectional study. Only 24.9% (n=217) of household supplies met WHO Guidelines of no detectable faecal contamination (thermotolerant coliforms (TTC)). Risk factors for intermediate and/or high risk contamination (11-100 and 101+ TTC/100mL) included low population density, increased open waste disposal within a sector, lower elevation, water sources other than piped to household or rainwater/bottled, and occurrence of an extreme rain event the previous day. Thus, community level factors are associated with stored household water quality; observed contamination poses a health risk in Rwanda. Matched Cohort Study: We next conducted a matched-cohort study in 18 villages to assess uptake, exposure, and health impacts of a water filter and improved biomass cookstove intervention programme 13-24 months after receipt. Coverage and use of the filter and cookstove was high, but non-exclusive. The odds of detecting TTC were 78% lower in the intervention arm (OR 0.22, p<0.001), with 50% lower odds of reported diarrhoea among intervention children <5 (OR=0.50, p=0.03). The intervention was associated with 43.4% lower fine particulate matter in kitchens (p<0.001), but geometric mean exposure remained above WHO targets for cooks (151 μg/m3) and children (175 μg/m3), and only marginally reduced among intervention cooks (22.2% lower, p=0.06). While the filter showed promise for health benefits, alternative household and community-level approaches for achieving clean, safe air are needed.