i use only distilled water. not even the "special" kind.. just grocery-ready bottles from wilkins or absolute. silver kill coils in some instances cause more harm than good. the SINGLE purpose of the kill coil is to prevent algae. so, unless your PC is getting direct sunlight, algae cannot grow. however.. since you now have SILVER in your loop.. you are now mixing metals. silver erodes the nickel plating on copper waterblocks. ive read EK denied RMA on gpu blocks due to corrosion on nickel plating because the user used a kill coil. that is also why there is hardly ever a warranty on water cooling blocks apart from defects "upon delivery" like cracks on nickel plating, mis alligned threading, shipping defects like bent rad fins, inlet/outlet ports and etc. you will never get an RMA if you corrode your block. (
EKWaterBlocks Support :: Knowledge Base :: Antimicrobial (algae) protection? )
so to make an already long story less long.. just practice proper and regular maintenance, regardless of what you use. water cooling is not a set-and-forget kind of thing. dont build a loop without a proper drain port to make life a little easier when the need arises. kung kapoyan mu ug huna huna sa maintenance, then i suggest you do not even bother getting started. look at it like a teenage pregnancy.. if you cant afford a child, then ayaw palabi habal. hehe. some users are really just better off sticking to traditional means of keeping there system in good condition.
edit:
adding to this.. bottomline is:
if you can, then do. in ANY hobby, when you ask "do i really need it?" is always irrelevant because in reality.. we never "really" do. BRUTAL TRUTH -keeping my system cool so it will last longer- or -perform better are just excuses we make to ourselves to justify the ridiculous amounts of cash we've spent for the hobby. iv'e accepted that a long time ago. kay kung "for having a long lasting pc" lang jud ang rason: i have a PC in the sala.. Pentium D. stock cooler. subject to daily abuse from my aunt, cousin and sometimes my kids. ive had it since 2005-6. still running. ive only had to replace the hard drive. even the generic PSU still kicks.
so again.. do it because you want to and can.