Super newb water cooling question

Do you need a reservoir for water cooling?

No, you can use a T-Line instead of a resevoir. Personally, I prefer a T-Line....it's what I use in my rig.

No but I think it's the easiest way to do it. The reservoir holds a bit of extra fluid witch is needed because water can slowly evaporate through vynal tubing over time. It also makes it a lot easier to get bubbles out of the system as they can float to the top when they reach the reservoir. Alternatively you can use a T line. Picture a T turned upside down with a cap on the top. It should be at the highest point in your system. The bit of tubing at the top of the upside down T has a cap and acts as a mini reservoir. You could get all the bubbles out of the system and make the last connection under water and have a closed loop but I don’t think this would work well over any length of time just considering changes in atmospheric pressure and dissolved gasses in the water.