16 Del. C. § 7934: Backflow.

(a) For purposes of this section:

(1) “Backflow” means the movement of water back in the direction from which it was flowing.

(2) “Backflow preventer” means a device that prevents backflow.

(3) “Backsiphonage” means backflow caused by negative pressure, which occurs when there is a drop in water pressure resulting in the water flowing back into the water service line.

(4) “Low hazard building” means a building in which any backflow that does occur meets the following conditions:

a. Occurs only by backsiphonage.

b. Does not create a health risk or health hazard.

c. Does not disrupt the service of piped water for human consumption or impair the potability of that water.

d. Does not pose a risk to any fresh water supply.

e. The pumping system involved does not connect to a treatment system used to convey wastewater, fertilizers, or chemicals, or that is used to provide fire protection.

f. The water system involved does not draw from more than 1 aquifer without a backflow preventer on the discharge line of each well.

(b) Subject to subsection (c) of this section, a county or municipality may not require backflow preventers to be installed or, if already installed, to be subject to inspections, in low hazard buildings of any of the following types:

(1) Single-family residences.

(2) Single-family residences with conditional uses that permit professional offices.

(3) Professional offices.

(4) Commercial buildings.

(c) If a low hazard building has fresh water supplied by a public well, backflow preventers must be installed in compliance with 7 DE. Admin. Code, Regulation 7301, governing the construction and use of wells.