Watermakers are not all created equally. Various Lagoon 42's have different models.

There was issues with factory installed water makers from what I have read on other sites.

And you are incorrect regarding not having 2nd water tank if watermaker present.

Sea Tiger has a Spectra Newport 400 watermaker which is highly regarded and has not had any issues (Installed post factory). Sea Tiger has second water tank for total 150 plus gallons.

I know of several 42s with extra water tanks (TMM Fleet).

BreckSailor... Pick your boat carefully and day one, ensure watermaker is working correctly.