Analyze Your Home's Water Usage

Do you want to reduce your home´s water consumption but you don´t know what action would have the most effect? Should you buy an efficient clothes washer, replace your shower head, or replant your garden with drought resistant plants? You can determine the costs of the alternatives, but you don´t know how much water is being consumed by each area, so you can´t tell what the most effective action is. For example, I found that it didn't make sense to replace the washing machine in my home with a lower water-use one, because the current one uses less than 3% of our water.

This is an explanation of how, with an hour or two of time, you can measure where all the water´s being used in your home.

In front of your house there´s a water meter the water company uses to measure your total consumption so they can bill you. It probably looks like the one on the above. Every time the red pointer goes around once, you´ve consumed one cubic foot, or 7.48 gallons, of water. To measure most of your uses, you´re going to turn on the consumption point, and then watch the meter for exactly one minute to see how many cubic feet are consumed per minute. Of course no other consumption, such as flushing toilets, can be happening during the test, so it is best to do this when no-one else is home. Some water consumption points such as your clothes washer have a complete cycle. For these you need to look at the meter reading before and after a complete cycle. Note also that for these you need to record the odometer-like number, in addition to the tenths of a cubic meter the red arrow points to.

The table above shows what I got, as an example. The first row means that when I turned on the sprinkler in our front yard that covers the South end, and watched the meter for one minute, the red arrow went around 1.1 times. Multiplying 1.1 times 7.48 gallons per cubic feet I get 8 gallons per minute. The sprinkler timer is set to 5 minutes per day, 7 days a week, for this sprinkler valve. 8 * 5 * 7 = 288. 3,121 is the sum of the gallons per week column.

288 / 3,121 is 0.092, or 9%.

The Dish Washer row means that the difference in the meter reading between the start of the dishwasher and its completion was 1.2 cubic feet. We run it about 4 times per week. 1.2 times 7.48 gallons per cubic foot times 4 times per week equals 36 gallons per week, which is 1.2% of the total.

To calculate the toilet consumption I read the label on the toilets which says 1.5 GPF (gallons per flush). I estimated that we flush about six times a day. If this had been a high percentage user I might have put a log sheet next to each toilet for a few sample days, to get a more accurate reading of flushes per day.

When I graph the various uses, in order of their percentile impact, I get the following:

This information led us to focus on the top line items first. We´re replacing the sprinklers in the back with a new drip system. This sprinkler system was watering a lawn in addition to shrubs. We´re replacing the lawn with vegetable garden. We were surprised by the amount of water consumed by the kitchen sink. In the past when doing dishes we just turned on the water and let it run as we rinsed off the dishes and loaded them into the dish washer. This finding lead to the Instructable called "Kneed Water". The rear drip system is really covering a big area all around the house, so it´s probably not ripe for much improvement.

We wanted to validate our data by comparing it to our water bill for the period in which the data was collected. The bill said we´d used 36 CCF in 58 days. CCF stands for hundreds of cubic feet. The green part of the table on page two shows that our measurements summed to 3,121 gallons per week. Dividing this by both 7 days a week and 748 gallons per CCF, we get 0.60 CCF per day. Multiplying this by 58 days we get a total of 35 CCF for 58 days. 35 is pretty close to 36, so we felt pretty secure in our technique. The 1 CCF per 58 day difference could be explained by items we did not measure such as brushing our teeth, and washing the car. If the difference had been significant, we would have measured those items too.

One challenge may be to open the lid of the concrete box where the water meter sits. A large screw driver or big pair of pliers is useful for this, as shown in the photos above.

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