Quantification of luminal water components provides tissue information in prostate MRI. The luminal water fraction (LWF) summarizes the amount of ‘luminal’, or longer T2 material in a distribution of tissue T2s. The parameters of this T2 distribution are found by fitting to the MR signal acquired from a multiple echo sequence. Iterative fitting of T2 distributions can be slow and different T2 distributions can give similar fits to data. The division into long and short T2 tissue for LWF calculations suggests that a simpler model may be effective. Two rapid alternative fits are presented.