"We all want to watch TV."
I would guess 要 applies for material stuff (要水) while 想 probably governs an action (想看电视) I'm just learning though, so don't take this by authority
For the specific sentence both terms could be used but they would have different meanings if you use 要 vs. 想. My understanding is that 要 implies someone/ones who wants to do something or needs to do something and will follow through with the action. Whereas 想 implies someone/ones who are thinking about doing something, a desire or feeling only. Here is a good video on it - www.youtube.com/watch?v=vb8BPhOohHs