Title explains it all.
I understand that those sailors could obviously not drink salt-water, but there were ways to use heat on salt-water and gather condensation to make fresh water (provided there was flammable material). I’d assume sailors back then also knew how to fish using large nets.
Besides dealing with scurvy, it seems those long voyages could be self sustaining and not be limited by water / food.
To reiterate and expand on my question: why was food and water often an limiting factor during those long voyages in the Age of Exploration? Did the people back then not know these methods of making fresh water? Was it hard to catch fish on those huge ships?
So, I answered a lot about food and water during Age of Exploration.
Here is my answer on the general food and diet of sailors but more importantly here is my answer on fishing that demonstrates with examples that it was regular to fish on the ships, and also this answer on water on ships where I even showcase the example of early 17th century testing of using a device for desalination of seawater (and the log noting it looks promising but is not efficient and provides too little water for the whole crew)
Indeed regarding your question on " why was food and water often an limiting factor during those long voyages in the Age of Exploration?" I would say the amount of times it indeed was the limiting factor was actually very rare, and as my examples in the answers above demonstrate, when lack of food or water was becoming critical, the danger indeed would be circumvented by catching fish for food and most usually capturing rainwater for water. With - also to be noted - even attempting to transform salt-water to fresh but which was determined to not be efficient enough to provide water for the whole crew.