The basic point is that if people collected rainwater instead of channeling it into the ocean they could have more than enough water. Don't argue at the margins and ignore the main point.
Yes, to solve the "drought" in a few short years, there are two basic tasks that California needs to undertake.
The argument made in the earlier part is clearly intended to be on-the-level as he assumes at this point that the reader is convinced by it enough to not call the current once-in-a-millenium drought a drought anymore.
But if we want to dwell on semantics -- a drought is defined as being an aberration from some norm. Given climate change, the drought in california isn't a "drought" but a change in norms -- this isn't a "once-in-a-millenium-drought" but, in fact, a new normal (didn't NOA just predict a multi-decade drought in California to be a virtual certainty in the next century?)