It's intended that the same character changes to a new playbook per the same rules as taking the advancement "change to a new playbook".

I'm not sure I fully grasp this Move.

Embargo: you can go aggro with deprivation as your weapon, inflicting d-harm (water).

Now, my first concern is that, if a Waterbearer in my game chose as their Source's special quality "It is the only reliable source of clean drinking water around" why can't they do what this Move says already? Within the fiction, when they threaten another character with deprivation, what happens? What do they roll? Does the target of their threat just believe the threat is empty because they don't have this Move?

The next would be this Move's interaction with the Go Aggro Move. So, per my reading of Go Aggro, say the Waterbearer rolls a 10+ and the target is an individual and chooses to "force your hand and suck it up" that individual will just die in three days. Just like someone cannot, once they "suck it up" with a shotgun aimed at their gut, avoid getting shot in the gut, a person cannot avoid dying of water deprivation if they "suck up" d-harm. Similarly, if it is aimed at a settlement, that settlement cannot send an armed contingent of goons to the Source to kill the Waterbearer and take it over, it has to find water elsewhere, because per d-harm, that is the only way to avoid the collapse of their settlement.

Am I reading this wrong? Go Aggro has always to me seemed like it should be played this way on a small scale, I'm just not sure whether it works on a long-term scale. Say the victim suffers d-harm from the Waterbearer, can another PC come along and give them water? What happens there? Similarly, is a Hold narratively incapable of gaining benefit from the water in the Source after they have suffered d-harm?

Any guidance on this is much appreciated!