How to Calculate Storage Need for Domestic Use

More is Not Better

Over the years storing water in unpressurized vessels has been looked on as a bad idea. Many believe that the mere contact of air with water will result in a contaminated supply.

Click this title to see Storing Water in Above Ground Tanks in the Applications section of this web site. When you're done reading that hit the back button and return here.

This reputation results from the common misconception that more is better. Storing too much water is not better; it is what causes the problems that some regulations seek to correct by insisting that water stored in an atmospheric tank must be chlorinated.

In some cases local rules governing the use of low yield wells say that atmospheric storage may be used to overcome a limited well yield but storage must be equal to a full day's water requirement or more.

One of the things we have discovered working with low yield wells since the mid 1990s is that the best way to prevent problems is to keep the tank active and cool.

The best way to accomplish that is to limit atmospheric storage to some amount close to peak demand need. Well Manager regularly adds water to storage so even tanks installed above ground in heated spaces do not warm up and since we limit storage, the content turns over several times per day thus keeping the tank active.

There is a serious downside to storing too much water.

1. There is the possibility of creating a breeding area for bacteria or algae.
2. A running toilet or other uncontrolled water use can empty the content of tank and well storage.
3. Water lost through running toilets ends up flooding your septic system.
4. Buried tanks with imperfect seals or cracks can admit shallow groundwater that is often contaminated

A properly adjusted Well Manager® cannot pump a well down because it is collecting yield only. If a toilet runs or a child leaves a hose on, the content of tank storage will be exhausted but storage in the well is not. Once the water waste is corrected, you can transfer water stored in the well to tank storage using the Manual function on the Well Manager control. This is why:

A Well Manager can provide more usable water, with less waste and fewer contamination issues, using less storage than other systems!

How Much Storage Does a Family Need?

The largest domestic water use for a home most often occurs in the hours between 6:00 AM to 7:30 or 8:00 AM. This is when everyone is showering and getting ready to go to work and school. How much water you need to store for your unique uses depends on:

1. The total amount required during this period
2. The duration of the peak demand period
3. The peak expected flow rate - how many bathrooms there are.
4. The well yield - how much water you can collect during that time

These same considerations must be examined for any use: restaurant, office building; school; church, etc., though some uses will differ in that they require a larger safety margin than others.

In the case of most uses that include bathrooms, the more there are, the faster you can use water. In a home, for instance, with four residents and one bathroom there will be only one shower occurring at a time. The same home with four bathrooms presents the possibility that all showers could be in use at the same time.

A 10-minute shower with a 3-gpm showerhead consumes 30 gallons of water. Though both the one and four-bath house will use 120 gallons showering, the former will use it over the space of an hour or so and the latter could use that much in ten minutes.

In reality, the people in the four-bath house probably aren't so regimented that this would happen but there will be some overlap and the duration of the peak demand period would likely be shorter.

The following spreadsheet can be used to calculate storage required for domestic or other uses supplied by a Well Manager® system. The results you obtain will also demonstrate whether the well you have can supply your need.

The results of the work sheet will produce a graph like this one, showing how your peak demand uses will impact the proposed storage arrangement.

You can download this calculating spreadsheet to determine the storage required with various well yields and peak demand needs. Once downloaded, the graph will instantly change to show the effect your proposed use and timing will have on storage using wells of various yields. The values in the yellow shaded cells are to be input by the user. You can rename the water uses and insert them at various times, alter the number of fixtures running (Number of Uses Column) at any given time and you can account for multiple fixtures running during the same time period by adding them together and entering that value in the appropriate cell in the "Gallons Used" column. Each row represents five minutes. A ten-minute shower with a 3-gpm head will require 30 gallons. Since the shower covers two 5-minute time intervals you would enter 15 gallons for each shower running during that time period in the appropriate cell in the column labeled "Gallons Used".

Uses like automatic clothes and dishwashers do not need all of the water to wash a load in the same time period. There is a fill/wash cycle and a rinse cycle. These may occur thirty minutes or more apart. To obtain a realistic picture of your need over time, enter these water uses in the correct time spot. See the operating manual for the machine you own. If you no longer have the manual, the manufacturer can give you that information.

Most dishwashers have a delayed start feature. Using this feature the dishwasher can be turned on before you leave in the morning but won't actually run until the time you have set, up to 4 hours in the future, arrives. This way you can get all your chores done even if there isn't enough water in storage to wash the dishes before you must leave for work.

Be realistic when reviewing your water use. Look at your family's habits in the morning. Some people jump right up and others need to be called several times so, even in a house with four bathrooms, uses will be staggered somewhat - in spite of the fact that everyone is supposed to leave the house at the same time. Take into account your toilets and your washing machine. Some toilets require 1.6 gallons per flush and some require 3.5 gpf.

It is also possible to determine the minimum well yield required to supply the proposed need. Simply change the value in the yellow cell below the "Well Yield in GPM" label in the section immediately below the graph and watch the affect different well yields have on the amount of water remaining in storage.

When you change well yield the amount of water the well will produce in a 20-minute, 30-minute, 60-minute, 24-hour, and 7-day period will recalculate. Play with the spreadsheet and you will soon realize that it doesn't take a lot of storage to get an amazing result when you collect the way a Well Manager does.