1. (a) “Air-gap separation” means a physical vertical separation of at least two (2) times the inside pipe diameter (or the largest inside pipe diameter, when multiple pipes are present) between the free-flowing discharge end of a potable water supply pipeline and the flood level of an open or non-pressurized receiving vessel, and in no case can the physical vertical separation be less than one (1) inch.
2. (b) “ANSI” means American National Standards Institute.
3. (c) “Backflow prevention assembly” means a mechanical assembly designed and constructed to prevent backflow, such that while in-line it can be repaired, and its ability to prevent backflow, as designed, can be field tested, inspected and evaluated.
4. (d) “Baffling factor” means the ratio of the actual contact time to the theoretical hydraulic detention time. For the purpose of these regulations, actual contact time is T10; and theoretical hydraulic detention time is reactor volume divided by flow rate.
5. (e) “Blackwater” means wastewater originating from toilets, urinals, and/or kitchen sources, such as from kitchen sinks or dishwashers.

6. (f) “Calibrated field meter” means a field test instrument (such as one used to test pH, temperature, dissolved oxygen, and electrical conductivity) that is used in accordance with the following conditions:

   1. (1) The instrument is field calibrated at the frequency recommended by the manufacturer prior to use;
   2. (2) The instrument is serviced at the recommended service frequency by the manufacturer or manufacturer-authorized service provider; and
   3. (3) Field calibration reports are maintained and available for inspection by the local jurisdiction for at least three years.
7. (g) “Certified backflow prevention assembly tester” means a person who is certified as a backflow prevention assembly tester by a certifying organization recognized by the State Board pursuant to the State Board's Cross-Connection Control Policy Handbook adopted pursuant to section 116407 of the Health and Safety Code.
8. (h) “Certified cross-connection control specialist” means a person who is a certified as a cross-connection control specialist from a certifying organization recognized by the State Board pursuant to the State Board's Cross-Connection Control Policy Handbook adopted pursuant to section 116407 of the Health and Safety Code.
9. (i) “Challenge test” means a study comparing a pathogen surrogate parameter, or indicator compound concentration between the influent and effluent of a treatment process to determine the removal capacity of the treatment process. The influent concentration must be high enough to ensure that a measurable concentration is detected in the effluent.
10. (j) “Commercial building” means a building, the operations of which will affect commerce and is intended for nonresidential use. For the purpose of this Chapter, commercial buildings do not include buildings or portions of buildings that are used for medical care, mental hospitals, other facilities operated by a public agency for the treatment of persons with mental disorders, adult care facilities, childcare facilities, and other buildings or portions of buildings serving similar functions and/or populations, as determined by the State Board.
11. (k) “Commissioning” means the procedures used by the responsible entity to inspect, test, and commence operation of an OTNWS and to train duly authorized agents or other staff to operate the OTNWS.
12. (l) “Community sewer system” means any system of pipes, pump stations, sewer lines, or other conveyances upstream of a wastewater treatment plant headworks that collects and/or conveys untreated or partially treated wastewater to a publicly owned wastewater treatment facility.
13. (m) “Continuous process verification monitoring” means ongoing confirmation of system performance using sensors for continuous observation of selected parameters, including but not limited to, surrogate parameters that are correlated with pathogen log reduction target requirements.
14. (n) “Critical limit” means a maximum and/or minimum value of a continuously monitored parameter which indicates that a treatment process or an operation is controlling the pathogen risk.
15. (o) “Cross-connection” means a connection or arrangement, physical or otherwise, between a potable water supply system and a plumbing fixture or a tank, pipeline, receptor, equipment, or device through which it may be possible for nonpotable, used, unclean, polluted, and/or contaminated water or other substances to enter a part of such potable water system under any condition.
16. (p) “CT” means the product of free chlorine residual and T10 measured at the same point, measured in milligram-minutes per liter (mg-min/L).
17. (q) “District-scale project” means an OTNWS for a defined service area and untreated alternate water source collection area that includes more than one multifamily building, commercial building, mixed-use building, or a combination of such buildings. A district-scale project may be located on one or more land parcels and may cross public rights-of-way.
18. (r) “Duly authorized agent” means a person legally designated by a responsible entity as having authority for the oversight and management of the OTNWS to ensure compliance with this Chapter. A duly authorized agent may be the same individual that is responsible for the operation and maintenance of the OTNWS collection, treatment, and distribution facilities. The authorization must be made in writing by the responsible entity and submitted to the local jurisdiction for local jurisdiction approval.
19. (s) “Field verification” means a performance confirmation study conducted using challenge testing, including surrogate microorganisms and/or other non-biological surrogates, during the commissioning period.
20. (t) “Graywater” has the same meaning as defined in section 17922.12 of the Health and Safety Code, which may include foundation drainage and condensate water.
21. (u) “Local jurisdiction” means a city, county, or city and county that has established a program for OTNWSs and has the authority to create, implement, and enforce the program requirements pursuant to subdivision (b) of section 13558 of the Water Code.
22. (v) “Log reduction” means the logarithm base 10 of the ratio of the levels of a pathogenic organism or other contaminant before and after treatment. A 1-log reduction is equal to 90% removal, 2-log reduction to 99% removal, 3-log reduction to 99.9% removal, and so on.
23. (w) “Log Reduction Target” or “LRT” means the log reduction required for the specified pathogen group to achieve an acceptable level of risk to individuals.
24. (x) “MBR” means membrane bioreactor, which consists of a biological treatment that is capable of reliably producing nonpotable water in which the organic matter has been stabilized, is nonputrescible, and contains dissolved oxygen, to feed into to its filtration process.
25. (y) “Mixed-use building” means a building that contains both multifamily residential and commercial uses.
26. (z) “Multifamily residential building,” as used in this Chapter, means a building containing three or more dwelling units and does not include townhouses.
27. (aa) “Nonpotable water” means water that is not suitable for human consumption. Human consumption is defined in subdivision (e) of section 116275 of the Health and Safety Code.
28. (bb) “Normal operating condition” means the operational condition where the treatment train influent and effluent quantity and quality are consistently within the expected operational parameters.
29. (cc) “NSF” means National Sanitation Foundation.
30. (dd) “NTU” has the same meaning as defined in section 60301.630.
31. (ee) “Onsite treated nonpotable water” means nonpotable water that has been collected, treated, and intended to be used on-site and is suitable for specified uses in Article 3.

32. (ff) “Onsite treated nonpotable water system” or “OTNWS” means a nonpotable water treatment system that does all of the following:

    1. (1) Collects and treats one or more of the untreated alternate water sources as described in subsections (a) and (b) of section 60610;
    2. (2) Distributes the treated water for use onsite (within or surrounding a building(s)) for nonpotable purposes; and
    3. (3) Serves a building or buildings that are connected to a community sewer system as the only means for discharge of waste, regardless of whether onsite wastewater is used as an OTNWS source water.
33. (gg) “Onsite wastewater” means comingled graywater and blackwater.
34. (hh) “Public water system” has the same meaning as defined in subdivision (h) of section 116275 of the Health and Safety Code.
35. (ii) “Regional Board” means any California Regional Water Quality Control Board.
36. (jj) “Responsible entity” means the person(s), corporation(s), or any other form of legal entity that holds a valid permit granted by the local jurisdiction to operate an OTNWS and has the necessary legal authority and control to ensure compliance with this Chapter.
37. (kk) “Roof runoff” means precipitation from rain or snowmelt events that is collected directly from a roof surface not subject to public access.
38. (ll) “State Board” means State Water Resources Control Board.
39. (mm) “Stormwater” means precipitation runoff from rain or snowmelt events that flows over land and/or impervious surfaces such as, but not limited to, streets and parking lots. Stormwater also includes runoff from roofs with public access.
40. (nn) “Supervisory control and data acquisition system” or “SCADA system” means a computer-monitored alarm, response, control, and data acquisition system used to monitor and adjust treatment processes and facilities.
41. (oo) “Surrogate parameter” or “surrogate” means a measurable chemical or physical property, microorganism, or chemical that has been demonstrated to provide a direct correlation with the concentration of pathogen; that may be used to monitor the efficacy of pathogen reduction by a treatment process; and/or that provides an indication of a treatment process failure.
42. (pp) “T10” means the time it takes for 10% of the incoming water to exit the disinfection reactor, measured in minutes.
43. (qq) “Treatment train” means a group or assemblage of physical, chemical, and biological treatment processes that conditions or treats water to achieve a specific water quality objective.
44. (rr) “Untreated alternate water source” means a source of nonpotable water that may include any of the following: graywater, roof runoff, stormwater, and onsite wastewater.
45. (ss) “UV” means ultraviolet light.
46. (tt) “Validation” means a demonstration of the pathogen or chemical contaminant reduction capacity of a treatment process.

Note: Authority cited: Sections 13558 and 13558.1, Water Code; and Sections 116271 and 116350, Health and Safety Code. Reference: Sections 13558 and 13558.1, Water Code; and Section 17922.12, Health and Safety Code.

History

1. New chapter 3.5 (articles 1-9), article 1 (sections 60600-60608) and section filed 4-22-2026; operative 4-22-2026 pursuant to Water Code section 13558(f) (Register 2026, No. 17).