"We actually have a section right below on the game page explaining the mechanics" -> You need not do that. Some levels before the current level 1 where each of these mechanics has to be used (alone) to open the door explains it sufficiently. You don't need text, just make one level for each such mechanic. Then the game starts easy and with satisfaction.
Regarding the Level 1 solution (thanks for the info): I am very sure I tried increasing the water level multiple times, but it only got higher once. So, when I pressed it again, it did not increase again/more. When using the inverse, the water got down, but funnily did not go away totally. Then, increasing worked again, but I only got the water up 1 brick level, never higher. I just played it again now, and it's the same problem. Am I still missing something, or is this a browser problem or something on my side?