Transparent World Water
A known limitation of GoldSrc is that it doesn't let you make the world water transparent. Xash3D makes this possible by adding the new variable sv_wateralpha, which adjusts water transparency. The value of this variable is stored in savegames.
Note: To fully support transparent world water, you need a special compiler that takes the transparency into account. Sample code for implementing this can be found in numerous compilers for Quake 1, where this feature has been enabled for quite some time.