The present invention relates to a 
system for monitoring quality of 
ballast water. The 
system comprises a central 
data hub comprising a 
data hub computer adapted for generating a set of acceptance criteria for 
ballast water quality parameters at one or more geographic positions based upon uploaded 
ballast water data from on-board computers of at least two vessels. The uploaded ballast water data indicates where, and possibly when, a volume of ballast water was loaded into a ballast water tank of each of the at least two vessels and the respective values of each of the ballast 
water quality parameters that are measured on each of the volumes of ballast water. The 
system for monitoring quality of ballast water further comprises at least two vessels, such as ships, each vessel comprising an on-board ballast water system comprises an on-board computer with a monitor, a 
data logger, a data storage for storage of a set of acceptance criteria for a number of the ballast 
water quality parameters corresponding to a geographical position and at least one geographical position. The on-board ballast water system further comprises detection means adapted for 
logging into the 
data logger the geographical position where the volume of ballast water is loaded into the ballast water tank and a number of ballast water quality sensors each being adapted for measuring at least one of the ballast water quality parameters of the ballast water in the ballast water 
piping or in ballast water tank. The on-board ballast water system is further adapted for 
logging ballast water data comprising a value of each of the ballast water quality parameters into the 
data logger and the on-board computer being further adapted for downloading the set of acceptance criteria from the central 
data hub and up-loading the ballast water data and the corresponding geographical position to the central data hub. The on-board computer is adapted to perform a comparison of the values of the ballast water quality parameters with corresponding acceptance criteria corresponding to said geographical position, and to display information on the monitor depending on said comparison.