The management of the Dutch national airline company KLM intends to bring a sufficient amount of water on board of all flights to fulfill customer’s demand. On the other hand, the surplus of water after a flight should be kept to a minimum to reduce fuel costs. The service to passengers is measured with a service level. The objective of this research is to develop models, which can be used to minimize the amount of water on board of flights such that a predefined service level is met. The difficulty that has to be overcome is the fact that most of the available data of water consumption on flights are rounded off to the nearest eighth of the water tank. For wide-body aircrafts this rounding may correspond to about two hundred litres of water. Part of the problem was also to define a good service level. The use of a service level as a model parameter would give KLM a better control of the water surplus. The available data have been analyzed to examine which aspects we had to take into consideration. Next, a general framework has been developed in which the service level has been defined as a Quality of Service for each flight: The probability that a sufficient amount of water is available on a given flight leg. Three approaches will be proposed to find a probability distribution function for the total water consumption on a flight. The first approach tries to fit a distribution for the water consumption based on the available data, without any assumptions on the underlying shape of the distribution. The second approach assumes normality for the total water consumption on a flight and the third approach uses a binomial distribution. All methods are validated and numerically illustrated. We recommend KLM to use the second approach, where the first approach can be used to determine an upper bound on the water level
