It certainly is not, no. Does this show with any project (e.g. even a small simple one) or only a specific bigger project? Can you pin down what actions can the memory to increase (debugging, building, editing)?
Keeping in mind also that for .NET, you cannot judge actual memory by what Task Man ager is reporting, as the runtime will hang on to “freed” memory for future use (but give it up if other processes use it). That said, if you’re experiencing slowdowns, than it most likely is a real leak.
Just for fun, can you try to avoid doing that for a day or two, and religiously close Water and/or start a new instance when switching projects,. and see if everything is fine then, or if memory issue within single solution is still an issue for you, over time?