For those of you that are concerned about the GPM of the pump vs the pproduction rate of the well. Here are some numbers you need to take into consideration.
Don't make the wrong assumption that capacity equals demand, or in other words, don't assume that because the pump can pump 20 GPM, that I am using 20 GPM. This is not practical reasoning. You have to consider these factor into the equation as well. The well has a reserve storage capacity of almost 58 cubic feet of water. The pump is at 100 feet which gives it 40 cubic feet of reserve water. 1 cubic foot of water = 7.48 gallons. So, 40 X 7.48 = 299 gallons (reserve water volume in the well above the pump). 299 divided by 20 = 14.92. So the pump could run wide open (under no head or tank pressure) for 15 minutes before it would exhaust just the reserve water. During that time period though, the well would have produced another 45 gallons of water (3 GPM X 15). This is not even calculating in the head and tank pressure which reduces the production rate of the pump to way below 20 GPM. The bottom line is, I would have to run the pump wide open for a bare minimum of 17 minutes to run the well dry. This will never happen because the pump is on a pressure tank system (with 100 feet of head) and the pump will only run long enough to build the pressure in the tank, which on a 100 gallon system like mine, might require 30 or 40 gallons to accomplish.
I am not saying that running the well dry can never happen, but it would not be because of the GPM capacity of the pump that caused it. It would be something unusual, like filling up a swimming pool or something. I don't have a swimming pool and I don't water my lawn (ever). Washing clothes and taking a bath at the same time is the heaviest demand this system will ever see, and while the demand may exceed 3 gpm during that short time period, there is way more then enough reserve in the well to make up the difference. So, the that I have a 5 gpm draw for a period of time, if the well is producing 3 gpm, then that is just a 2 gallon deficit and with 299 gallons of reserve, it would be a long time before the well went dry.
NOTE: I cam back and edited this because I made some miscalculations and forgot to subtract the 30 foot of well at the top of the well that does not contain water. But the main point I was making is still valid and is uneffected by this miscalculation.