Introduction:
Ships implement international standards to ensure the safety of potable water on board^1,2. Ships on international voyages are inspected to obtain a Ship Sanitation Certificate (SSC) under the International Health Regulations (IHR)³. During these inspections, potable water samples may be collected and analyzed for microbiological and chemical parameters. This study aims to analyze such results to identify factors contributing to positive microbiological and chemical results in water samples.

Methods:
Results on microbiological and chemical analyses of potable water samples from non-passenger ships between 2010 and 2018 were provided by the Belgian port health authority. The dataset included sample characteristics and laboratory results, while ship characteristics were sourced from an online database⁴. Deficiencies identified during SSC inspections were obtained from EU Common Ship Sanitation Database^4,5. Chi square test (and fisher test for values below 5%) was used in order to identify possible risk factors. Logistic regression was used for the multivariable analysis. Statistical analysis was performed using R Software.

Results:
Between 2010 and 2018, a total of 5538 potable water samples were collected during 3497 SSC inspections aboard 2066 ships. General cargo ships had a higher risk of positive microbiological samples compared to other ship types. However, multivariable analysis did not identify statistically significant associations between ship type and microbiological contamination. Ships with at least one deficiency related to potable water safety had three times higher risk of positive samples compared to those with no deficiencies (RR = 3.68, p-value < 0.001). For chemical parameters, the risk of contamination was over four times higher in ships older than 12 years.

Conclusions:
Recommendations for public health authorities include:

• Prioritizing microbiological sampling of potable water on ships where at least one relevant deficiency, particularly deficiency 9.18.8 (coloured water), has been identified.

• Prioritizing chemical sampling of potable water for ships older than 12 years.