The earlier part of this report showed how roof venting - if extensive enough - could remove all the combustion products of a fire. If this was not enough to prevent spread altogether, wetting down of fuels heated by radiation could prevent their ignition. However, venting induces draughts towards the fire and if these are strong, weak water sprays can be deflected into the fire, where they would be less effective. An attempt to use the minimum effective water quantities for wetting down may thus be ineffective. This report describes experiments on the deflection of water curtains by an air stream and shows how the effect can be calculated with the necessary degree of accuracy so that the data reported can be provisionally extrapolated to situations other than those examined experimentally. With draughts of up to 1.2 m/s, a water flow of 0.5 m^-1s^-1 can give sufficient width of wetted fuel 5 m below the nozzles to prevent fire spread.