Detection Limits for Purposes of Reporting (DLR)


DLRs are the designated minimum levels at or above which any analytical finding of a contaminant in drinking water resulting from monitoring must be reported to the State Water Board. The DLR represents the level at which we are confident about the accuracy of the quantity of contaminant being reported by laboratories. The DLR is typically set equal to or below maximum contaminant levels (MCLs) but is often above the contaminant public health goal (PHGs). Of 92 existing contaminant MCLs, 49 have DLRs set above their corresponding PHGs. (View a list of all regulated chemicals’ MCLs and PHGs).

Under Health and Safety Code 116365, the State Water Board is required to review MCLs at least once every five years and consider revisions to an MCL if there are any changes in technology or treatment techniques. While analytical methods are available to report data at concentrations lower than the current DLRs, many water systems and laboratories report concentrations only as low as the DLRs. The lack of occurrence data at concentrations below current DLRs impairs the State Water Board’s ability to evaluate whether technology can achieve a materially greater protection of public health or attainment of the PHGs. To adequately evaluate health risk and technological feasibility of a revised MCL, DLRs should, where feasible, be set at concentrations at or below the corresponding PHGs.

DLR Regulations


  • Metal Detection Limits for Purposes of Reporting

The metal DLRs regulation proposes to lower the DLRs for the following metals with primary standards: antimony, arsenic, beryllium, cadmium, lead, mercury, nickel, and thallium. The draft proposal would revise DLRs for these metals to concentrations closer to, or equal to, the corresponding PHGs. Additionally, the regulation proposes to establish DLRs for iron, zinc, and manganese (metals with secondary standards) to ensure that methods used in performing required analyses are sufficiently sensitive to ascertain compliance with those standards. View more information regarding this draft regulatory proposal.


  • Perchlorate Detection Limit for Purposes of Reporting

The current perchlorate MCL is 0.006 mg/L. In 2015, OEHHA revised the perchlorate PHG from 0.006 mg/L to 0.001 mg/L. The regulation proposed a Phase I perchlorate DLR of 0.002 mg/L and Phase II perchlorate DLR of 0.001 mg/L, effective January 1, 2024. The perchlorate DLR regulation was approved June 17, 2021 and effective July 1, 2021. More information may be found on the DDW Perchlorate DLR Regulatory Proposal page.

Future Work

DLR revisions for radionuclides, volatile organic compounds, or synthetic organic compound may be considered.