How much water does a family of five need?
Let me first ask if there is a way to search previous community questions and answers? I don’t want to take people’s time if a question has already been asked and answered.
Our family of five is building a new house in Zone 5A within the next six months. There’s no water available, so we have to choose between a well and a cistern. We are leaning towards a cistern because of the potential unknowns associated with a well (will it contain arsenic/radon, will we need to drill multiple times, what’s the flow rate, what if it goes dry in the future, etc…)
One issue that has us reconsidering the well is that our house will have a relatively small roof cross-section (on the order of 2000 square feet), so during the dryer winter months we will only harvest about 4000 gallons a month from rainwater collection (we’re planning on a 5500 gallon cistern). Currently we use about 6000 gallons a month, but we make minimal efforts to conserve water and have an inefficient toilet and washing machine. I’m wondering how much water a family of five might use if they have a high efficiency front loading washer, pressure assisted toilets, and faucets/shower heads with modest flow rates. I understand that the number is “it depends,” so I guess I’m looking for water conscious people in similar situations to ask whether 4000 gallons a month is a realistic target or a pipe dream (pun intended). Our kids are small now (ages one to six), and I would guess that their water consumption will increase as they age?
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Replies
This really is a it varies problem.
That said you have your numbers for now, you can work with them. Determine how much your washing machine uses per load (most water meters can be read) and how many loads a week. My top load high efficiency uses about 80-100L a load. A high efficiency front load can use 30-60L/load.
Count how many times your toilet is flushed a day and how many liters it uses. Don't assume its faceplate number of liters is correct.
Also do you wash dishes by hand or dishwasher. Determine water used either way. You can probably take the Energy star guidelines of a dishwasher at close to face value, but how often it is run will matter.
Do you water your lawn?
Do you have a water softener?
Any other water users?
How many and how long are your showers/baths, check the liters used, the shower head will have a rating but differing pressure means you need to measure it as well
Basically do an audit of everything, determine how much you use and where, and you can determine how much you can save and what your final results will be.
As for the future that is hard to say but including your kids in this from understanding the problem to measuring to conserving will help them learn how to adjust their usage and keep it in check over time and teach the value of conservation.
I'd check with local well owners. Is it common to be unable to hit water? What is a typical well depth and what does it cost? Do deep wells in your area ever go dry? Our well in Maine is about 400 feet deep and cost about $5000 three years ago. Around here, deep wells never go dry, but your location may be different.
A cistern will not be cheap and I suspect you may need more than 5500 gallons. You'll also need to filter, clean and purify the water coming off your roof.
Joe,
Cisterns are common in the Caribbean, and on islands with few options for water. Anywhere that a well can be drilled, however, most people choose to drill a well rather than depend on rainwater. Remember, there is a strong possibility that rainfall amounts will change in the future due to global climate change.
In areas of the world where families have to haul water in buckets, families quickly learn how little water is actually needed to sustain human life. So the answer to your question is clearly, "It depends."
As Alan pointed out, many families use a lot of water to water the lawn, water the vegetable or flower gardens, or wash their car(s). These uses greatly affect average water use.
The average for residential water use in the U.S. is 80 to 100 gallons per person per day (for a family of 5, that translates to 12,000 to 15,000 gallons per month).
The amount of water used per person per day varies by climate. In some states, like Vermont, the average is less than 75 gallons per person per day; in other states, like Utah, the average is more than 150 gallons per person per day.
If we think in terms of families rather than individuals, statistics stay that the average American family uses 300 gallons a day -- equal to 9,000 gallons a month.
Joe,
Here in the wet PNW cisterns aren't unusual. But even here they are problematic, mainly because even though they are typically sized in the 10,000 to 15,000 range, they often run dry in the summer months.
Another thing to remember is that they definitely affect re-sale value, as a feature that eliminates many potential buyers.
You may want to consider having 2 cisterns 1 for potable water use that for sinks and washing machines directing there drains to the gray water cistern and using that water for toilets and landscaping. So you can use your water twice.
What is the annual rain fall where the home will be built?
Walt
Holly cow, 15,000 gallons per month?!
How can that be possible?
Davor,
The 15,000 gallons per month figure was due to a mathematical exercise. Clearly a family of 5 that includes three young children does not use as much water per capita as a family of two that includes 2 adults. A 4-year-old doesn't wash cars and rarely has a separate vegetable garden that needs watering, so, on average, a 4-year-old American uses less water per day than an adult American.
Not 15000 gallons per month.
15000 gallons is not always enough to get past a dry season 90 -180 days without running empty.
Walta
We have a somewhat efficient washer and dishwasher, low-flow heads on faucets and showerheads, and the toilets, while not extreme water savers (no dual flush or anything), are recent and somewhat efficient. We don't water the yard to speak of. This year our family of two-sometimes-three averaged a bit under 3,000 gallons a month (so at most, neglecting the third person entirely, ~50 gallons per person per day), and last year our family of two-sometimes-four-or-five (adult children in and out, home from college and so forth) averaged about 4,050 per month (~67 gallons per person at most). Of course that includes some times when we were away, but we don't travel a ton and we do fairly often have house guests, so I think it should even out (especially as during any longer trips we have a house sitter, who presumably bathes and so on).
Looking at bills from when we had three teenagers (well, two and an almost-teen) at home, they are not as much higher as one would think. Average a tad under 5,300 gallons a month. (We definitely had some months over 6,000, though.)
Also, to answer your first question, there is a search box at the upper right of the QA page. A question like this might be hard to find precise keywords for, though. I just tried [water usage gallons person] and a lot of the results were obviously irrelevant.