I would say that the Captain/Owner should have planned for a minimum of four gallons per, day per person, plus a ten day reserve. This is a lot of water, and I know the boat would not be able to carry that much, so there is an issue from the start. I wonder why the owner of a race boat would not go with a three day sized tank and a watermaker that would fill it with a short time of running the generator or engine every day to keep it topped off? That would keep the weight lower, and help them make the passage more comfortably.
No way. Surely that was in jest.
We, as cruisers with kids and a fat Bulldog don't go through anywhere NEAR that much water... even with showers and washing dishes in fresh water. Realistically, we can make it 14 days @135g with good conservation. Good conservation is salt water washes, fresh water rinses, and very brief showers which likely wont be everyday. If we take showers everyday and fresh water washes and are generally non-conservative, we are about 10-12 days. If we had to, we could push the two week limit (and if we were crossing the ocean, we would have to). In the marina, we can go under the 12 days - esp if the kids do the dishes.
Now, in fairness, we do drink gatorades and keep water bottles around for hikes or outings. But we also drink alcoholic beverages and we will generally keep a 5g bucket of water with ammonia in it for washing which could get refilled depending on spaghetti-to-mouth malfunctions. SO realistic numbers are 8g/day for us pretty conservative but comfortable. This will include the periodic showers and fresh water rinses for dishes. Also, as you increase the people, you can decrease some of the water/pp. THis is because a single person may still have to fill the 5g bucket of fresh water or the sink for rinses. But that same water can be used by others without decreasing the supply.
You also need to add into this discussion (as Jane pointed out) that you will be getting water from foods. If you eat a can of brothy soup, you probably are not going to drink a large cup of water afterwards. SO depending on the foods (excluding alcohol, that is ridiculous), you may not use as much water. Also, your suggestion for a 10 day reserve on top of that is ludicrous. Using your numbers, some boats may not even carry 10 days worth of water for that crew!
Regarding the watermaker, there is no way in Hades that I would have the lives of my crew dependent on a mechanical piece of equipment that could fail without warning. Like Nick did, I would have it as a backup, not as a primary use. If he says he can do it, and has done it, on 1g of water/person - I will take his word for it. THat would not be my comfort level, but with severe conservation, I can see how that could work (also including food/soups and excluding alcohol).
My opinion (and real life experience).