So much depends on your deck
set up, but can you catch rainwater on deck? This is a safe and mostly reliable option if you let the rain wash the salt
off, plugs the deck drains and then open your intake drain. We had a 3 inch teak
toerail which allowed for a substantial amount of rainwater to accumulate. We could fill our tank in a few minutes.There are also simple awning setups that can be rigged quickly when it starts to rain. This can be the safest option in Mexico
or other places where amoebic dysentary is endemic.
Once in a desparate no-rain situation in the Tuomotus, I fished a dead rat out of the village's cistern, jerry canned water to the boat and chlorinated the heck out of it. Small hand pump filters are readily available today to backpackers that filter out giardia and other tiny critters. There's no reason not to have a variety of options on board. Water is life.