If you're doing your holes for fixtures and fittings through glass then you are best off with diamond drills.
We do an "all in one" solution for about £7.15 per drill via the £49.99 BFKMX
The beauty of this system is that it Will GRIND the glass rather than drill it giving you perfect (chip free) workmanship. Also works on other tile types like porcelain, granite, travertine, marble and ceramic.