Chance of Contamination Entering Well From a Water Storage Tank

Is there an increased chance of contamination entering back into the well from a water storage tank that refills with a float set up rather then installing a back flow preventer? How difficult is it to check a back flow preventer once a year?

What is the potential of a 2,500 gallon buried white plastic water storage tank becoming contaminated with it's float set to refill the tank after 300 gallons have been drawn off knowing the total monthly water usage is only 1,000 gallons per month?

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The fact that the tank is underground helps. Keeps it cool and out of the sun. You may not have a problem with contamination but, I would have a water test done to be sure. Pumping water into the top of the tank with an air gap would keep the tank from being able to drain back down the well. If the tank doesn't feed from the top, a good check valve or BFP is needed.

If it makes a difference, the tank is only in the ground half way, apparently they hit Caliche (calcrete). The top half of the tank is covered with 6 inches or so of dirt. Location is in Phoenix with Desert temperatures.

Do you mean a check valve or BFP on the feed to the home? There is also a pump from the storage tank feeding a pressure that feeds the home.

Thank You!!

Even 6" of cover will help keep it cool and keep the sun out. Both of these things help reduce the possibility of contamination. A check valve on the pressure pump is needed or the pump will just continue to cycle on and off. A check valve on the well pump is needed to keep the storage tank from draining back down the well.