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→Calculating Water Capacity
The literature on water consumption is all over the map. Experienced yachtsmen on cruising sail boats can manage on 1.5 gal of water per day per person, for all needs excluding bathing and dish washing; although 3-6 gal is more common.
Other yachting estimates are as high as 15 gal a day per person. At the other extreme, one 400-passenger cruise ship, the <i>MV Millennium Queen</i> (believed broken up in 2001), budgets budgeted 60 gal per day per passenger, which is close to domestic consumption. Domestic consumption is a benchmark for a live-aboard, but estimates still vary widely.
For a standard office, guidelines are 25 gal/day per person but have been shown to be as low as 6.8 with conservation measures [3]. Of course, office estimates don’t include cooking, showering and washing clothes, etc.
Vendor specifications also indicate that many marine toilets require 3-5 gal per flush, with the most efficient (VacuFlush) requiring only 0.375 gal (0.8 L). The more profligate ones can use seawater but VacuFlush requires fresh water [49].
Other sources estimate that domestic hot-water consumption alone runs 20-35 gal/day per person, with a peak demand of 10 gal [?]. To meet such a peak demand, the [[HotWaterHeater|hot water heater ]] must deliver 10 gal/person at any time. Additional capacity is needed for appliances, such as dishwashers.
Other capacity recommendations for hot water tanks range from 7 gal per person [2] to as high as 17 gal.
In tests in my apartment taking showers not baths I observed a daily consumption of about 40 gal. Taking a bath (52-in bath) quickly jacked the number up into the NRCan realm. These are the results of the tests:
* Bathing** Bath 21-42 gal, or** Shower 20 gal/d (2 @ 10 gal)
* Toilet 10 gal/d (8 @ 1.6 gal)
* Dish washing 4 gal/d (4 @ 1 gal)
* Household cleansing 0.25 gal/d
== Reduce Consumption == Water consumption can be reduced using (descending order) water-efficient shower heads, toilets, dishwashers, clothes washers, and automatically closing taps. Low-flow shower heads alone can reduce water usage by 30%. Older shower heads deliver 4 to 5 gallons (15.1 to 18.9 litres) of water per minute. However, the USA Energy Policy Act of 1992 sets maximum water flow rates at 2.5 gallons (9.5 litres) per minute at a standard residential water pressure of 80 pounds per square inch (552 kilopascals). == Conclusion ==
Before doing the above test, I had settled on 25 gal/person/day as a design goal. Afterwards, and because water capacity is so critical for a live-aboard, I increased this to 60 gal/person per day overall. With a 250-gal water tank, this gives a base cruising capacity of two days for two people. A 500-gal tank would provide the same for four people. A watermaker would have to supplement this for extended cruises
== Tank Overflow ==
The fresh water tank should have an overflow outlet overboard. Boats have been sunk at the dock when connected to shore water that overflowed the tank in one way or another.