This study presents a new analytical model for the prediction of the critical heat flux (CHF) in water saturated flow boiling in round vertical and uniformly heated pipes. The CHF is assumed to occur in annular flow when the liquid film vanishes at the exit section of the heated channel. Channel pressure drop is calculated using the Friedel correlation. Liquid film flow rate is obtained by a balance of liquid entrainment and droplet deposition. Two mechanisms are considered in the calculation of the entrainment: liquid-vapour interfacial waves and boiling in the liquid film. The model CHF prediction values are compared with a data set of 5159 selected experimental points for water, showing a good agreement both in precision and in accuracy for liquid quality in the range 0.2-1.0.