Large customers although small in number represent a significant portion of water volumes registered by meters in a water supply system. As a result, an improved large meters management can provide, with limited effort, excellent results for recovering commercial losses. This particular feature is acknowledged by many water utility managers which select this type of meters as the starting point of their programs for improving meter management. Although, in essence, the principles of large water meters management are basically the same as the ones applied to small meters, large customer meters require specific and particular care. It should not be forgotten that the amount of money involved in economic transactions between water utilities and large customer does not allow for any miscalculation. The slightest error drift may lead to a considerably economic loss. This is why installation and acquisition costs of large meters are in most cases negligible with respect the value of the water sold to the customer. Consequently, large meter replacement programs should always analyze the total costs of the meters, i.e. initial costs (understood as the initial acquisition and installation costs) plus the costs related to the operation of installed meters that include not only maintenance costs but also, as it has been said, the cost of the water volumes used by the customers and not paid for. In Arregui et al. (2011) a graphical method to calculate the optimum replacement period of water meters was presented. The proposed chart was the result of a mathematical model which considered all economic costs taking part in the life cycle of a water meter.