Water is the most important part of a cruising boat. Your boat needs it to float and you need it to live! Being how this is such a vital resource, getting it, managing it, and storing it should be the most important thing on a boat.
Fresh water is available at most ports, but some places will charge you to fill up your water tanks. You should make sure you like the water before you put it in your tanks. If the water is dirty or contaminated, it could make a mess inside your water tanks. Another important quality of the water is taste. You will be drinking this water and you should enjoy it. If the water tastes horrible, it will make everything miserable! If you don't like the water, it may be best to wait and search for a different source of water; as long as you have enough to get you there.
The next most common method to get fresh water is to make it yourself with a water maker. Water makers apply tremendous pressure to sea water and force pure water through membranes, leaving very salty brine behind. As you can imagine, this process requires a lot of electricity. If you have the means to meet its electrical demands, a water maker can alleviate your water needs. The only weak link in a water maker are the membranes. These filters are prone to clogging if the water is not clean and they can become damaged if the unit is not used often enough.
While a water maker will represent the potential for thousands of gallons of water, these are all "potential" gallons. If the water maker breaks, you are left thirsty. For this reason, you should never remove a water tank, which offers "actual" gallons, to use the space for installing a water maker.
The last way to get water is to collect it as it falls from the sky. In areas with heavy rainfall, rain collection will provide a steady flow of water in a daily fashion. Methods to collect rain water vary and are greatly dependent on the layout of your own personal yacht.
Being how water is such a crucial and vital resource on a yacht, it should be guarded and used as such a resource. You wouldn't dump gold into the water, so why would you leave your faucet on and dump your fresh water overboard?
Conserve the water you have on board and protect it, as it is a very valuable resource. When you have the opportunity to get more, examine it and make sure you want to add it to your tanks.