<p>Child mortality has been a global concern, the rate of which is seen to be higher in developing countries, particularly in Africa. The rate of mortality of under-five is alarming in Nigeria as the source of causation particularly in relation to water and hygiene appears to receive little attention. Thus, this study examines the impact of water and hygiene on child mortality in Nigeria. Poisson technique was applied to analyze household survey data obtained from the Multiple Indicators Cluster Survey. Our results revealed that water and hygiene have significant impacts on under-five mortality. The incidence ratio of handwashing is associated with a proportional increase in death among children under-five. Its average marginal effect signals a serious concern, indicating that handwashing habit is associated with 40 under-five deaths per 1,000 before the fifth birthday. Also, water is found to have a detrimental effect on child mortality, its incidence ratio indicates that unprotected source of water increases child mortality. In furtherance, mother’s education suggests a low incidence rate of child death if the level of mother’s education is high, vis-à-vis. The average marginal effect shows the rate may reduce by 30 deaths per 1,000 if the mother is educated. In contracts, we found that the fertility rate may not pre-empt child mortality, as population is not significantly associated with mortality. For preventing water- and hygiene-related diseases, some important action plans are commended.</p>