Foams play an important role in a wide range of processes. In these processes the foams are often flowing and the amount of liquid carried within them is an important operating consideration. In froth flotation, for instance, the amount of water collect is intimately related to the amount of gangue collected, which in turn helps dictates the grade of the product obtained. This paper presents some theoretical relationships for the prediction of water recovery from a flowing foam. In the foams that have less than half the bubbles bursting at the top surface, the amount of water collected is independent of the amount of bursting and the rate is proportional to the gas rate squared and inversely proportional to the bubble diameter squared. When more than half the bubbles burst, there is a similar dependence on air rate and bubble size, but the fraction of the bubbles that bursts becomes a further factor. This relationship is demonstrated experimentally to provide a very accurate prediction for stable 2-phase foams. The relationship is theoretically applicable to the 3-phase froths found in flotation, but there are a few problems involved in obtaining the correct variable values to put into the relationships. The most problematic of these is the average size of the bubbles that are collected to the concentrate. It is also demonstrated how this equation can be used as an alternative method to image processing for estimating the bubble size in flotation froths. (C) 2003 Published by Elsevier Ltd.