That was some incredibly risky storytelling. I get that they want to make the audience question Carrie, but we already do and I get that they want Carrie to probably evolve this season and learn to love her baby. And I get that Carrie is very unstable...but you cant have your main character start the process of drowning her baby. You just cant. Especially in season 3. Especially when carrie already has so many skeletons and flaws.
Plus, it makes her sister seem very irresponsible. She knows Carrie is unstable. Why the **** would she leave the kid with her?
That was just a scene they shouldnt have went with unless their ultimate goal is to make Carrie suffer some serious Karma this season. If thats their goal and they want us to really hate her and want her to fail horribly as a human being and as a CIA Chief then they are off to a great start.