Sample Size Calculation The sample size of the stepped wedge trial was calculated based on the primary objective: reduction of systolic blood pressure. Data from southwest Bangladesh suggest a 7 mmHg lower mean systolic blood pressure among pregnant women who drank pond water compared to those who drank brackish water, and a 17 mmHg lower mean systolic blood pressure for pregnant women who drank rainwater compared to those who drank brackish water. The mean reduction in systolic blood pressure following long term modest salt reduction is 4.2 mmHg. At least three mmHg of systolic blood pressure reduction has been considered for the current study among the communities who will have access to MAR water for drinking and cooking purposes compared to those who will use brackish water. The entire population under the catchment area of an MAR community will be considered as one cluster. Each MAR community serves approximately 300 people, constituting 60-70 households in the catchment area. The mean household size in southwest coastal Bangladesh is 4.2; approximately 52% of household members are ≥ 20 years. Since blood pressure will be collected for all household members ≥ 20 years, an average of 2.2 participants has been estimated to be in this age group per household. About 28 households per cluster (28 *2.2 = 60 people per cluster) will be selected for the study. A previously published study in Bangladesh reported standard deviation (SD) for systolic blood pressure as 13.51. The sample size of the stepped wedge trial has been estimated adopting the formula used by Woertman et al. 2013 and Hemming et al. 2015. Woertman et al. proposed the usual approach of initially calculating the sample size for a simple unadjusted trial (NU), and then multiplying by the design effect for stepped wedge trial (DESW). The sample size of simple unadjusted trial was 1,868 participants (effect size= 3, standard deviation of 20 for both groups, 80% power, and 5% Type I error). The DESW was 3.046 based on formula provided by Woertman et al 2013. Considering a fixed cluster size of 60 and 5% loss-to-follow up, the proposed study will need 20 MAR communities, with five communities randomized to access MAR water in each step.