Globally, many millions of people still lack access to safe drinking water and sanitation facilities. Here, we examined associations between household availability of improved drinking water and sanitation, respectively, and use of maternal and child health (MCH) services in South Asian countries. Demographic and Health Survey population-based data from Bangladesh, Nepal, India, and Pakistan were used, restricted to women with a child aged 0–36 months (n = 145,262). Types of households’ water source and sanitation facilities were categorized based on the World Health Organization and UNICEF’s definitions of “improved” and “unimproved”. We applied logistic regressions to estimate odds ratios (OR) and 95% confidence intervals (CI) for improved water and sanitation, respectively, and reported antenatal care visits, having a skilled attendant at birth, and infant vaccination coverage, stratified by maternal education. Among lower educated women, access to improved water source was associated with greater ORs for presence of a skilled attendant at delivery and their children having up-to-date immunizations (OR: 1.29; 95% CI: 1.17, 1.42). Among lower and higher educated women, improved sanitation (vs. unimproved) was associated with greater ORs for having had adequate antenatal care visits (OR: 1.74; 95% CI: 1.62, 1.88; OR: 1.71; 95% CI: 1.62, 1.80), and similarly for having had a skilled attendant at birth, and children with up-to-date immunizations. Approaches addressing water/sanitation and MCH services across sectors could be a suggested public health strategy.