Interesting, I actually did run around it and couldn't see the flicker, and I do have an nvidia. Figured it was nothing since others were seeing it. Though this still doesn't explain why it hasn't come up in another map...
setpos -3258.833984 312.407867 263.969666;setang 2.002001 -1.539999 0.000000
setpos -3257.744873 352.902405 263.969666;setang 2.002001 -1.539999 0.000000
setpos -1881.607422 116.749626 159.849731;setang -12.782001 -33.263981 0.000000
setpos -1881.607422 116.749626 159.849731;setang -15.708003 -29.259991 0.000000
setpos -202.937622 -98.394867 320.969666;setang 2.618002 -1.848010 0.000000
setpos -121.966064 -101.007423 320.969666;setang 2.618002 -1.848010 0.000000
Not quite sure whats going on, but here's what I noticed.
For me, it appears to change brightness based on if the water could be seen in the view frustum.
You have two brushes of expensive water next to each other at different heights.
In t7 you switched to water_2fort_expensive from water_2fort in t6.
And switched to water_2fort_skybox_dx80 from water_2fort.