Actually, I'm not sure. 30% of alcohol drinkers being addicted might be roughly right (though surprising to me as well).
In the US, 50% of Americans hardly drink at all (under 0.15 drinks/week). But 10% of Americans drink a staggering 75 drinks a week, or over ten drinks a day every day (where a drink is a can of beer, glass of wine, or equivalent). [1]
Of course you can't determine from that alone whether those people are clinically addicted, but it sound reasonable to me that most are. Further, probably some proportion of people in the other groups are also addicted, but not drinking nearly as much.
So that's 10%, and only 50% of Americans are drinking at all, so that's 20% of drinkers are drinking 10+ drinks a day, and some unknown proportion have alcohol problems while drinking less.
1. https://www.washingtonpost.com/news/wonk/wp/2014/09/25/think...