The Lead and Copper Rule works differently from almost every other drinking water regulation. Most rules set an MCL and measure compliance in finished water at the treatment plant or entry point. The LCR measures compliance at the customer's tap, because that is where the problem occurs. Lead and copper do not come from the source water. They come from corrosion of plumbing materials between your plant and the glass someone drinks from.
That distinction matters for the exam and for how you think about your job. As a treatment plant operator, you control water quality leaving the plant. You do not control the pipes it flows through on the way to a customer's faucet. The LCR is the regulatory framework for managing a contaminant source you cannot directly access, and it does that through a sequence of escalating requirements triggered by action levels rather than MCLs.
Let me walk you through how the rule works, what the action levels mean, and the response sequence the exam expects you to know.
Why Does the LCR Use Action Levels Instead of MCLs?
The LCR uses action levels because lead and copper contamination occurs in the distribution system and customer plumbing through corrosion, not in the source water or at the treatment plant. An MCL measured at the entry point would not capture the actual exposure. Action levels measured at the customer's tap trigger the utility to take treatment actions that reduce corrosion throughout the system.
That is a fundamentally different regulatory approach. With an MCL, you either meet the number or you are in violation. With an action level, exceeding the number does not mean your water is illegal. It means you are required to take specific corrective actions. The distinction matters for the exam: action level exceedance triggers requirements, not violations.
California implements the LCR through Title 22 CCR sections 64670 through 64696. The rule applies to all community water systems and nontransient noncommunity systems.
Action levels are triggers, not limits. This is one of the most commonly tested distinctions on the T-5 exam. If a question asks what happens when the lead action level is exceeded, the answer is a sequence of treatment and public education requirements, not an MCL violation.
What Are the Lead and Copper Action Levels?
Two numbers. Memorize both.
| Contaminant | Action Level | Detection Limit for Reporting (DLR) |
|---|---|---|
| Lead | 0.015 mg/L (15 ppb) | 0.005 mg/L |
| Copper | 1.3 mg/L | 0.050 mg/L |
Both are measured at the 90th percentile of first-draw tap samples. That means 90% of the samples you collect must be at or below the action level. If the 90th percentile value exceeds the action level, the system has an action level exceedance.
The Lead and Copper Rule Improvements (LCRI, finalized in 2024) also established a lead trigger level of 0.010 mg/L at the 90th percentile. This is a lower threshold that initiates additional planning and communication requirements even when the action level itself is not exceeded. Think of it as an early warning: your lead levels are not high enough to trigger the full response sequence, but they are high enough to require attention.
The exam frequently asks for the lead action level (0.015 mg/L) and the copper action level (1.3 mg/L). It may also ask about the LCRI trigger level (0.010 mg/L for lead). Know all three numbers and what each one triggers.
How Do You Calculate the 90th Percentile?
The 90th percentile calculation determines whether your system exceeds the action level. The process is straightforward, and the exam may ask you to perform it.
Step 1: Rank all tap sample results from lowest to highest. Step 2: Multiply the total number of samples by 0.9. Step 3: The value at that position in the ranked list is the 90th percentile. Step 4: If the 90th percentile is greater than the action level, you have an exceedance.
Take a concrete example. You collect 20 samples. 20 times 0.9 equals 18. Rank all 20 results from lowest to highest. The value at position 18 is your 90th percentile. If that value is above 0.015 mg/L for lead, you have an action level exceedance.
For very small systems serving 100 or fewer persons that collect only 5 samples, the 90th percentile is calculated as the average of the highest and second-highest results.
Any result below 0.001 mg/L is treated as zero for the calculation.
How Does First-Draw Tap Sampling Work?
First-draw sampling is designed to capture the water that has been sitting in contact with plumbing materials the longest. That is where lead and copper concentrations are highest.
A 1-liter sample is collected from taps served by lead plumbing, lead solder, or lead service lines. The water must have been standing for at least 6 hours, which is why samples are typically collected first thing in the morning before any water is used.
The 6-hour standing time is not optional. It is what allows lead and copper to leach from the plumbing into the water. A sample collected after the customer has been running water all morning would show lower concentrations and would not represent the actual exposure risk.
The first-draw protocol is a common exam topic. The key requirements are: 1-liter sample, taps with lead-bearing materials, water standing at least 6 hours. The exam may present scenarios where one of these conditions is not met and ask whether the sample is valid.
What Is Corrosion Control Treatment?
Corrosion control treatment is the primary tool for reducing lead and copper at the tap. It works by adjusting water chemistry to form a protective scale on the interior surfaces of pipes, preventing lead and copper from dissolving into the water.
The most common CCT approaches are pH and alkalinity adjustment (raising pH to reduce the aggressiveness of the water toward metal pipes) and adding corrosion inhibitors such as orthophosphate or silicate compounds. The goal is to create conditions where a stable, protective mineral layer forms on pipe surfaces.
The State Board designates optimal water quality parameters (WQPs) that the system must maintain once CCT is installed and optimized. These parameters include pH, alkalinity, temperature, calcium, conductivity, and orthophosphate or silica concentration (if used as an inhibitor). Maintaining these parameters within the designated ranges is an ongoing obligation, not a one-time demonstration.
Optimal CCT is defined as treatment that minimizes lead and copper at taps without causing the system to violate other drinking water standards. You cannot solve a lead problem by creating a different compliance problem.
What Happens When the Action Level Is Exceeded?
The LCR defines a specific response sequence. Each step is required only if the action level remains exceeded after the previous step is completed. The sequence escalates from treatment optimization through infrastructure replacement.
Step 1: Corrosion Control Treatment. Study the options, recommend optimal CCT, install it, and demonstrate optimization. For large systems (over 50,000), a CCT study is mandatory. For small and medium systems, the State Board may designate optimal parameters without requiring a study.
Step 2: Source Water Treatment. Required if the action level is still exceeded after CCT is optimized. The system must monitor lead and copper at entry points and install treatment if source water is contributing to the problem.
Step 3: Lead Service Line Replacement. Required if the action level is still exceeded after both CCT optimization and source water treatment. The system must replace lead service lines on a defined schedule.
Step 4: Public Education. Required whenever the lead action level is exceeded, regardless of which step the system is on in the response sequence. The system must provide specific health effects information and steps consumers can take to reduce exposure (flushing, using cold water for cooking).
Consumer notification is also required: individual tap sample results must be provided to each sampled customer within 30 days, including health effects information. All lead and copper monitoring, treatment, and reporting records must be retained for 12 years.
There is no safe level of lead exposure. Lead is most dangerous to children under 6 and pregnant women. The exam may test your understanding of why lead is treated with such urgency compared to other contaminants.
What Are the Lead Service Line Requirements Under LCRI?
The Lead and Copper Rule Improvements (LCRI), finalized in 2024, significantly strengthened the service line requirements.
Systems must develop and maintain a complete inventory of all service lines, categorizing each as lead, galvanized requiring replacement, non-lead, or unknown. The inventory must be publicly accessible. This is a nationwide infrastructure mapping effort that many systems are still completing.
When the action level is exceeded, systems must replace lead service lines in their entirety, including both the utility-owned portion and the customer-owned portion. Previous versions of the rule allowed partial replacement (utility side only), which could actually increase short-term lead exposure by disturbing the pipe without removing the customer-side source. The LCRI eliminated that practice.
The Lead and Copper Rule operates on a fundamentally different principle than most drinking water regulations. The contaminant source is between you and the customer, not in your source water. The response is a sequence of escalating actions, not a binary pass/fail. Understanding that framework will serve you on the exam and in your career.
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This guide is for educational purposes and reflects federal and California regulations as of April 2026, including the LCRI. Always verify current requirements with your state regulatory agency.
Frequently Asked Questions
What is the lead action level under the LCR?
The lead action level is 0.015 mg/L (15 ppb) at the 90th percentile of first-draw tap samples. It is not an MCL. It is a trigger for treatment, monitoring, and public education requirements. The LCRI also established a trigger level of 0.010 mg/L that initiates additional planning even when the action level is not exceeded.
How is the 90th percentile calculated for lead and copper?
Rank all tap sample results from lowest to highest, then multiply the total number of samples by 0.9. The value at that position is the 90th percentile. If it exceeds the action level, the system has an exceedance. For very small systems collecting 5 samples, the 90th percentile is the average of the highest and second-highest results. Results below 0.001 mg/L are treated as zero.
What is corrosion control treatment and when is it required?
CCT is required when a system exceeds the lead or copper action level. It involves adjusting water chemistry (typically pH/alkalinity adjustment or adding orthophosphate/silicate inhibitors) to form a protective scale on pipe surfaces that prevents lead and copper from dissolving into the water. The State Board designates optimal water quality parameters that the system must maintain.
Why does the LCR use action levels instead of MCLs?
Lead and copper enter water through corrosion of plumbing between the treatment plant and the tap. Since utilities cannot control customer plumbing, an MCL at the plant would not address actual exposure. Action levels measured at the tap trigger utilities to take system-wide corrosion control actions that reduce leaching from all plumbing materials.
What are the lead service line replacement requirements under LCRI?
The LCRI requires systems to inventory all service lines (categorizing as lead, galvanized requiring replacement, non-lead, or unknown), make the inventory publicly accessible, and replace lead service lines in full (both utility and customer portions) when the action level is exceeded. Partial replacement, which could increase short-term exposure, is no longer permitted.