Fresh water is the most valuable resource on board a boat! Without it, you will die in as short as 3 days, while some have managed to survive as long as 8 to 10 days without fresh water. This is why deciding how your fresh water is stored is so important.
Some boats have one large water tank which holds all of their available fresh water. This makes filling up easier, as it is only one tank to manage and maintain. This also fits the old saying "Putting all of your eggs in one basket" to the tee. If that tank were to break or get contaminated, you now have lost all of your water!
The alternate option is to break the water stored into various tanks, this way if a tank gets damaged or contaminated, it only affects that one tank and not the entire water supply.
The disadvantages of multiple tanks are:
You now have many tanks to maintain and keep full.
The advantages of multiple tanks are:
Evenly distribute the weight around the vessel
If one tank is damaged or contaminated, it only affects a portion of the total water supply
It is easier to monitor how fast you are consuming your water
It is easier to ration your water
On board Wisdom, we have 8 water tanks, totaling up to 160 gallons of fresh water.
Tank 1 is 15 gallons, 120 pounds
Tank 2 is 15 gallons, 120 pounds
Tank 3 is 30 gallons, 240 pounds
Tank 4 is 20 gallons, 160 pounds
Tank 5 is 20 gallons,160 pounds
Tank 6 is 30 gallons, 240 pounds
Tank 7 is 15 gallons, 120 pounds
Tank 8 is 15 gallons, 120 pounds
This may sound confusing to manage, but it works out well. We can easily ration our water by only using one tank at a time. We have an idea of how long we want each tank to last, and if we burn through the water too fast, we are made very aware of it when it runs dry.
The act of opening a new tank also lets us keep a mental picture of how we are consuming our water. When we did our summer trip, we started off with Tank 1 open, and it lasted us almost a week. This made us a bit more relaxed about our water usage (which translates into more frequent showers). We keep Tank 6 (30 gallons) as a backup tank while cruising. If we ran out of water while off shore, Tank 6 would be able to provide us enough drinking water for 28 days (based on 2 people drinking 2L of water per day).
The final advantage of multiple tanks is that the weight can be spread throughout the vessel. 160 gallons weighs 1280 pounds! If we had that all weight in one place, it would seriously affect the trim of the vessel as it ranges between full and empty. By spreading the weight around, the weight is also evenly distributed and we are able to drain the tanks in a controlled fashion, which also evenly distributes the weight decrease.