In fusion devices the hydrogen Balmer lines are used to measure the neutral flux from the walls into the plasma using the atomic physics factor S/XB. This is a standard diagnostic which can be applied in ionizing plasma using , or without knowledge of the electron density. We will extend this method to a recombining plasma in front of a surface. can be used in an analogous way to measure the plasma flow to this surface which can be e.g. a divertor target. The other Balmer lines are not suitable because the corresponding atomic physics factor R/YB depends on density due to three-body recombination. An application of this diagnostic method is provided.