How much water do you use?
 

Trying to calculate the size of a back-up cistern or underground tank for my desert home. What are the minimum (monthly) water requirements for two people (showering, laundry, flushing)?

Depends what you are looking for.

US or Ethiopian standard ? :D

U. S.

It's more than you might assume. About 50-60 gallons per day, per person average.

A typical American or Canadian might use 50 to 60 gallons per day and in super conservation mode maybe 20 to 30 per day. So if you settled on 50 per day, x2 = 100 per day for 2 people or 3000 gallons per month. That comes from Environment Canada. Broken down to 40% flushing, 33% bathing, 17% laundry and the rest for cooking and drinking. No washing cars or watering you cacti included. They say one typical car washing is 120 gallons!

Sounds good. And, if I take a dump at work & pee in the backyard, I could probably knock off another 10 g's/day...

Lets see now I flush about 8 times aday...now wait a minute sometimes I gotta double flush so that puts it at about 12 times a day....I only shower once every 2 weeks...so that should come toooo.....

Water dept estimates 75 gal/day each person.

Our family of 4 averages both children (girls) with frequent bathing.

170 Gallons per day total. averaged over 4 years.

Go with two 1000 gallon tanks in series w/feeder lines. Send all your gray water to the garden and you'll never have a problem unless you start leaking from your toilet flapper and do not change it out when you notice the leak......

My calculations indicate I can fit a 5,000 gal. tank or cistern in the backyard. I will install some sort of pump/filter system. The water won't be of drinking quality, but if there is a shortage, at least I'll be able to stay in the home.

Gray water will be diverted to a sump and filtered into the desert.