To get an idea of how using rainwater from rain barrels will impact your overall water use, you need to have some idea of how much water you currently use each year without a rain barrel. First off, track down your utility bills if you rely on municipal water. You will need to refer to them for your calculations. If you have your own well, this step will be a bit more complicated, so we’ll address it in the next section.
Your utility bills are usually calculated in CCF (The first ‘C’ represents the Roman numeral C, which equals 100; the second ‘C’ stands for cubic; the ‘F’ stands for feet.) One CCF equals 100 cubic feet of water, which is equivalent to 748 gallons.
If, for example, you have used a total of 110 CCF for the year, you can multiply 110 x 748 to determine the number of gallons.
110 CCF x 748 = 82,280 gal
Using our previous calculation of 24,000 gallons of rainwater collected for our theoretical house, if your current use is 82,280 gallons, it may appear that collecting rainwater wouldn’t have a significant impact. However, household usage doesn’t change much during the year, but landscape usage will vary considerably. In many areas the largest amount of rain falls in the winter, so you probably wouldn’t immediately use the rainwater for landscaping until it gets drier. By following the steps below, you will probably see that a lot of your water usage, up to fifty percent or more, is from watering your garden during the dry months.
Check your water bills again and look at how much water you use in the rainy season. Also refer once again to the average rainfall for your area that you calculated previously. With this information in hand, you can now estimate how much water is used in the house as opposed to the landscape.
By turning on each water faucet in the house and measuring how much water comes out in a given period of time and then estimating how many minutes each faucet is used each day, you can have a pretty good idea of indoor usage. For example, turn on the water in your shower and catch it with a one-gallon container. If it fills up in thirty seconds, you know that a shower will use two gallons per minute. Now estimate the amount of time spent in the shower by members of your household.
You’ll also want to measure toilet water usage. You can check your toilets by turning off the supply valve and flushing the toilet. Use your one-gallon container to fill it back up. That will tell you how many gallons it uses for each flush. Multiply the number of gallons by the number of flushes per day to get your estimate. You may also want to consider changing to a lower use water tank for your toilet to save even more water. There are low-volume flush toilets available that use around a half a gallon of water per flush!
Now that you’ve calculated your household use as compared to your landscape use, you will see more clearly the benefits of a rain barrel for collecting rainwater. By using the 24,000 gallons of harvested rainwater during the dry season, you will greatly reduce municipal water system stress. Also, because many municipalities charge extra for high water usage during the summer, you may see additional savings during the summer months.