I was wondering do you need any type of mods to the ecu (utec, exede, etc..) to run the aqaumist 1s water injection? What size jet should i use?

 

ah ha!
You could get a flash on your ecu for leaner fuel and maybe a bit of timing. That would be the least expensive approach.
I use the #8, but I bet you there are many different thoughts on what works best. The right choice would be to study the charts and read the posts on the aquamist posting page.
http://www.aquamist.co.uk/phpBB2/index.php

 

A .8 is a good size for a stock turbo'd Evo. I recommend the XEDE or something that has map switching capabilities. I am going to run some safety "stuff" on mine that will switch to the secondary "safe" map if something bad happens (blocked jet, bursted line, no water).