I agree the mass fractions would be one way. Where the mass of the stream per meter, if it were 100% water, would be such, but in reality the mass per meter of stream, is diluted by the steam. Temperature of the steam gives the density of the steam, and the difference between the steam mass per volume, and the mass per volume of the water, is the shortfall, which percentage makes up for the dilution about. So divide the mass shortfall per meter, by the density difference per meter for the volume percentage steam versus water. Easy from there. If that's what Hamed said, Kewl