"Evaporative cooler water use" by Martin Karpiscak and Mary H. Marion at
http://ag.arizona.eduj/pubs/consumer/az9145.pdf cites a survey showing
an average water usage of 7.6 gph, which seems like a lot compared to the
7.6 gpd below. And these things have 1/2 to 1 HP motors.

Most home coolers have 1/2 HP or less.

A Las Vegas homeowner might do better with Sam's portable 797895 Arctic
Breeze cooler mounted inside a house near an open low window and
That unit may be able to cool a 9 x 9 room. Not much more than that.

an exhaust fan in a higher window with a one-way plastic film damper.
Have you lived in Las Vegas or anyplace in the Southwest?

You can't recycle the air in the house. You have to get rid of the moist
air as it will not cool.
That's what the exhaust fan does, controlling the indoor RH precisely with
a humidistat, vs a swamp cooler without a humidistat.
But the air is already quite humid when it enters the house.


Turn on the cooler when the house temp reaches 80 F and turn on the
exhaust fan when the RH reaches 60% to keep the house air at the upper
right corner (80 F and w = 0.012) of the ASHRAE 55-2004 comfort zone.

For an average good cooler pulling in 110 degree air at 10% humidity will
lower the temperature to 80 degrees. The exhaust fan is working all the
time if that dinky portable cooler can handle the load. Anyway a normal
cooler which costs about the same will do the job.

The maximum cooling is when the humidity is very low. Once it gets to
30% cooling becomes marginal.
You are thinking about the air outside vs inside the house.
No. At 110 degrees and 30% humidity the air coming out of the cooler is at
90 degrees. You can calculate it's relative humidity at that time.

Keeping that house 80 F while evaporating P lb/h of water into C cfm of
outdoor air means 1000P = (91.1-80)(128+C). P =
60C(0.075)(0.012-0.0066)
= 0.0243C makes C = 108 cfm and P = 2.62 lb/h, ie 7.6 gallons per day.
If the house has significant thermal mass (eg a floorslab), we can save
more water and energy by only running the cooler at night.

Have you ever lived in the Southwest where the overnight temperature does
not get below 90? Most all houses in that area already have slab floors.
The solution would be to move underground for the summer.
And, I will agree that during the part of the season where the temperature
does not get below 90 you may indeed us 7 gallons an hour to cool a 2000
square foot house. In that climate we usually set the thermostat at 80 or
above.