Just water and exersise alone is really a no-no ....as when the body doesnt get carbs...its starts to produce fat in the belly region.
Ask any person who is Hypothyroid.
They will tell you that their appetite is down YET they still gain weight.
I have heard of people going on a 'soup ' diet made from nothing but fresh vegetables and this detoxifies the body as well as it being a diet agent.
Research more into it.
But also remember, we have germs in our bodies that we need to filter the bad toxins out too.
There are different thoughts about "detoxing", but I'm not sure exactly what you are talking about. Are you planning ONLY to drink water and exercise 3 days/week as your detox? If that's the case, it wouldn't really be considered a detox. Drinking plenty of water is very good for you to make sure you stay hydrated. And of course, exercise is imperative to a healthy life style.
From articles I have read, most doctors will tell you that your liver and kidneys are the only detox needed since they filter impurities from your body. The only way this would not be sufficient is if you have a problem with you liver or kidney function.
Congratulations on trying to quit smoking. I quit a couple of years ago - your body will get rid of the toxins and it doesn't take very long for you to start feeling better - at least it didn't for me.
I'm not real familiar with a vegan diet, but again, your body will get rid of the "bad" stuff you've eaten.
On the other hand, there are some people who swear by detoxing and I would guess it's pretty much a personal choice. I HAVE tried it a couple of times but didn't really see that it did any good. Just remember that some methods of detoxifying can be dangerous, so be careful in what you choose.