We used the ammonia method (learned right here on CF!) on our recent trip to the Bahamas
. It worked great.
We often used local well water (like at Shroud
Cay) that we might not want to drink, but was fine for washing
clothes. This really saved our finite drinking water
The ammonia method is great for getting body odor
out of clothes. But it doesn't "get your whites their whitest," so after a few weeks or months, you might want to do a load with bleach instead. That ought to evaporate just as ammonia does.
Also, ammonia doesn't remove sun-screen stains, which all our shirts eventually got around the necklines. Those needed to be scrubbed out with Joy first, but that could be done in salt water