Ill. Admin. Code tit. 35, § 604.1515 – Agency Approved Cross Connection Control Measures

a) For all mains, pipes, structures through which water is obtained and distributed to the public, including wells and well structures, intakes and cribs, pumping stations, treatment plants, reservoirs, storage tanks and appurtenances, collectively or severally, actually used or intended for use for the purpose of furnishing water for drinking or domestic use, cross connection devises must be used as set forth in this Section.
b) Except as provided in this Section, a fixed air gap must be used.
c) Atmospheric vacuum breakers may be installed subject to the following conditions:
1. 1) the location is not subject to back pressure;
2. 2) the substance in the container receiving water is not toxic; and
3. 3) an atmospheric vacuum breaker is installed at the highest point in the waterline and after the last control valve before the point of discharge and a minimum of six inches above the flood level rim of the receptacle.
d) Examples of acceptable installations of atmospheric vacuum breakers include:
1) surface wash piping for a gravity filter;
2) solution tanks of gravimetric dry chemical feeders;
3) faucet with hose attachments; and
1. 4) receptacles with a low-level inlet where the substance contained is nontoxic, such as food or beverages.
e) Reduced pressure principle backflow preventers may be installed subject to the following conditions:
1) Installation
1. A) Units must be accessible for maintenance and testing.
  1. B) Minimum clearances recommended by the manufacturer must be used.
2. C) Units must be protected against flooding and freezing.
  1. D) Relief ports must not be plugged. A drain that will remain free flowing under all conditions must be provided.
  2. E) No reduction must be made in the size of the relief port drain.
3. 2) Bypass lines without reduced pressure principle backflow preventers must not be installed.
4. 3) Reduced pressure principle backflow preventers must be used for installations where a fixed air gap is not possible, and an atmospheric vacuum breaker is not allowed under subsection (c).