  Theoretical cross sections for the pressure broadening by hydrogen of
rotational transitions of water are compared to the latest available
measurements in the temperature range 65-220 K. A high accuracy interaction
potential is employed in a full close coupling calculation. A good agreement
with experiment is observed above ~80 K while the sharp drop observed
experimentally at lower temperatures is not predicted by our calculations.
Possible explanations for this discrepancy include the failure of the impact
approximation and the possible role of ortho-to-para conversion of H2.
