How far upstream should charities operate?

If a charity working on reducing heart disease, for example, found that they could add a medication to the global water supply and completely eradicate heart disease from the human race, should they do it?

Ethics (not giving people a choice) and consequences (increasing the human population) aside, should they do it? I say these things aside because I’m interested in how far upstream charities could go to solve problems rather than whether they should.

It seems to me that most charities act on problems at a down-stream point closest to the impact, and not many take solutions upsteam to prevent the problem form happening. And from the charity’s point of view this makes sense, because how can you demonstrate the impact you’ve had on a problem that doesn’t exist because you’ve fixed it upstream? Better then, to have a problem that exists and support the people facing that problem.

Upstream problems require complex systems changes, and perhaps many charities feel unable to act in that space, or that it’s not their role to do so. I wonder if this is where charity innovation needs to go?