A very similar procedure is followed to determine the extinction coefficient etc. in H2O. Here, the laserball is required to be in the light water region between the AV and the PSUP, and PMTs are considered which lie within 200cm of the vertical axis which passed through the laserball position. The resulting quantities, OCA_H2O_EXT(IW,1) and OCA_H2O_EXT(IW,2) (along with OCA_H2O_ISO(1) and OCA_H2O_ISO(2)) are also specified in OCA_OUTPUT.INC.