A big YES to this one. I've heard all kind of stories around this, and most of the people i know says that is OK to run without it, but for personal experience i can say this will lower the life expectenacy of your turbo, and this is increased when running high boost... Anyway, i'm sending a link from Garrett where it explains why you need your water lines and i thought it would be a good read for everyone in the forum (couldn't find if this was posted alread). Enjoy!
http://www.turbobygarrett.com/turbo...iles/Garrett_White_Paper_01_Water_Cooling.pdf
http://www.turbobygarrett.com/turbo...iles/Garrett_White_Paper_01_Water_Cooling.pdf