To the OP:
My short answer: allocate 1 gallon (4 liters) of water
per person per day, for all uses. Also give them each a personal and smaller water
bottle for handy drinking, and encourage drinking fresh water over other beverages. Take additional water as a reserve, just in case the voyage takes longer than expected.
I think the smart thing to do is give each person a clean one gallon plastic jug with a screw on top, and their name printed on it in permanent marker. Fill it each day with fresh water. That is their days ration for all uses of FRESH WATER, aside from cooking
. Also, encourage all crew to drink water rather than sodas or anything alcohol or anything diuretic (teas or coffee). Reason? Because the body needs water, and dehydration is bad and can be debilitating. Many of the foods eaten on a passage
will be salty processed foods.
Anticipate that bad things can happen to your engine
that may prevent using a watermaker
and that you might take longer to reach your destination
. Be prepared with enough tankage or jerry cans of fresh water to make it to the destination
with some buffer or reserve.
My Experience Anecdote: I was on a sailboat crossing from Hawaii
. It was expected to take 21 days or so, because we were going to motor
when needed through the low wind
areas, and so we took plenty of fuel
. It turns out that about 3 days into the voyage we could not use the engine
at all! The trip took 30 days, and could have taken longer as we essentially sailed the whole way, aside from being becalmed for several days. After 20 days of sailing, and still not knowing how much longer till landfall (10-15 more days?), we began to ration the water. I learned about real thirst then, and eating salty canned foods and crackers, which was was all we had left in the galley
stores, served to worsen this. Also, the water in the boat tank was very foul as we got to the bottom of the tank. It was so disgusting that no one wanted to drink it at that point. It had heavy green algae and was the consistency of pea soup.
My water lessons learned?
Have more water than you think you will drink for a voyage that could take longer than average for that route
and that boat. You should drink more water than you normally do in a city, because your exposure to the sun and wind
and physical activity may make you more thirsty. Avoid beverages that cause more thirst. Have backup water in separate tanks
or cans or jugs. Have an easy way to allocate fair rations each day at a set time (I suggest morning) for everyone in the crew. Use identification on personal water jugs. Anticipate that mechanical systems (engine or watermaker) CAN fail. Have more water, rather than spare watermaker parts
as a backup. It may be other systems (engine) which may prevent the use of a watermaker if your boat has one.