If you think of an easy way to nail together a short wall like that and how to make it difficult, which would a builder choose? The easy way if it fits the local code!
That leaves it easy to see building the wall as a simple rectangle with a stud or two where it meets the main wall and then more studs every 16 inches along the short wall. Framing guys can almost look at a stud and tell you where 16,32, and 48 are going to be so they are not going to cheap out and try to make it some different number between studs. US tape measures come with those point having special marks so we can find them--- just in case it was built by a "new guy"!
That leaves the left side of the tank setting directly on one or possibly doubled studs and another just 16 inch out, so the tank is nearly on top of two 2X4 capped with a 2X and then the countertop.
The corner crack? Things just move enough to crack the sheet rock mud at the corner. Looking at the picture, that is even less worry as it is simply a trim board with a sliver out of the side and only serves as an easy way to hide the rough cut edge of the drywall which is then attached to the horizontal wood underneath.
NO hazard at all.