First, before I forget it, is a link to a YouTube evaluation of a watermaker, made by Greg & Jill Delezynski. You might want to look for more of their videos, they are very helpful to the cruising community. Watermaker evaluation
Because we do not have a watermaker and I don't plan to have one again, all I can offer are some links to watermaker sites.
And here's Greg's gear report: Guenevere's 2006 Gear Report
When we sailed from Ecuador to Easter Island, which took 19 days, there were three of us on board. SV Watermelon had 75 gallons (~285 liters) of water tankage. Another 10 gallons (40 liters) in jerry jugs. We had some left when we made landfall. I've read of even greater water economy from other cruisers, but we bathed as we traveled. In all the years we cruised outside the US, only once did we worry about not having any fresh water, and we were luckily saved by a local island trading freighter with "buckets" of water.
I would think that 2000 liters could get you almost across the Pacific in one go. I would think, though, that you could reduce the amount of water you carried (and thus reduce weight) if you could desalinate water as you go. Watermakers are extremely power-hungry, though, so you had better have a good generator.