Jul 11 2014
Water-The Third Rail Part XV
In the July 9, 2014 San Diego Union Tribune on the front page is a story
about the deepening drought. In the Business section is an announcement of a
new 332 room hotel. No problem, since we have limitless water supplies,
right? Wrong! This new hotel will hook onto the existing system of imported
water into San Diego and consume about 560 acre-feet a year.
Unless the developers have discovered an artesian well under the hotel site. 1,200
single family homes will just have to do without water to supply the new
hotel. An acre foot is the water needed for two families for a year or half
an acre foot per family.
It is often said that Californians live in LaLa Land. I am beginning to
believe it. Oh, I forgot, by 2035 we are going to start recycling a fraction
of the wastewater being dumped into the ocean according to the San Diego
County Water Authority. No problem for those of us who will have gone to our
For the engineering inclined, here is the calculation:
Per the Uniform Plumbing Code, for each room that has a lavatory, toilet and
shower there are 7.5 fixture units. A fixture unit is a measure of how much
water will be used. So for 332 rooms, 2,490 FU.
Add about 20% for back of the house usage (restaurants, pools, etc.), and
offset an 80% occupancy with a contingency factor and applying the number of
gallons per fixture unit, the 332 rooms will consume 420 gallons per minute.
A six inch diameter water service line will handle that much water.
Multiplying by 60 minutes per hour and 24 hours per day yields 604,800
gallons per day. Let’s be conservative and round that down to 500,000
gallons per day, or 0.5 million gallons per day.
So in a year, the new hotel will use 0.5 times 365, or 182.5 million
gallons. Although the units are often mis-stated, when you see so many
acre-feet used, the correct way to show that is acre-feet per year. Dividing
182.5 million gallons by 326,000 gallons in an acre foot, the result is 559
Acre-Feet per year.
The San Diego Water Purification Pilot Plant is lauded to produce a whopping
one million gallons per day. Sounds like a lot. Actually the new hotel will
use half of all that plant can produce. The output of that plant doesn’t
sound like so much now.
I am thinking San Diego could be a bonanza for the people who make underarm
deodorant when three million people start taking one minute showers so the
developers can build that hotel.
About Alumni at the University of Montana