Introduction: Health and diseases on board ships may depend on water. Interventions to improve the quality of water may bring to significant benefits to health and water stores/supply and should be controlledto protect health. This paper has reviewed the main regulations for the control of water safety and qualityon board ships and presents some practical recommendations for keeping water healthy and safe in passenger and cargo merchant ships.Methodology: The main international regulations and guidelines on the topic were analysed. Guidelines forWater Quality on Board Merchant Ships Including Passenger Vessels of Health Protection Agency, World Health Organisation (WHO) Guide to Ship Sanitation, WHO Guidelines for Drinking Water Quality, WHO Water Safety Plan and the United States Center for Disease Control and Prevention Vessel Sanitation Program were examined. Recommendations for passenger and, if available, for cargo ships were collected and compared. Recommended questionnaire: A questionnaire summarising the main information to collect for assessingthe enough quality of water for the purposes it should be used on board is proposed. The need of havinga crew member with water assessment duties on board, trained for performing these activities properlyis discussed.Conclusions: Water quality on board ships should be monitored routinely. Monitoring should be directedto chemical and microbiological parameters for identifying possible contamination sources, using specifickits by a designed crew member. More detailed periodic assessments should be under the responsibility ofspecialised personnel/laboratories and should be based on sample collection from all tanks and sites of waterdistribution. It is important to select a properly trained crew member on board for monitoring water quality