/usr/share/gromacs/top/amber99.ff/watermodels.dat is in gromacs-data 4.5.5-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | tip3p TIP3P TIP 3-point, recommended
tip4p TIP4P TIP 4-point
tip4pew TIP4P-Ew TIP 4-point optimized with Ewald
spc SPC simple point charge
spce SPC/E extended simple point charge
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