The number of samples and measured values for lead and copper (analyte) levels in public water supplies can be found with our Drinking Water Watch application.
Sampling: Ten to 30 separate samples are taken from different parts of a water system to provide complete picture of water quality. Drinking Water Watch reports the number of samples taken for each water system. Lead and copper amounts in every sample are measured.
Measurement (90th percentile method): Lead and copper values are measured for each sample taken, and the 10% of samples with the highest amounts of lead or copper are averaged. This average of the highest tenth percentile is reported as the measure of lead or copper for the system. This measure is used to determine whether action needs to be taken to lower lead or copper levels in the water.
Measurement (95th percentile): Samples also have the highest 5% of samples measured. Because they represent a smaller group of the very highest lead or copper amounts found, they are normally higher than the 90th percentile measure. This measure is for informational purposes, and does not require any actions to be taken by the water system.
Action levels: Lead and copper measures each have an action level. Sample that rise above this level require the water system to take actions to notify the public and reduce the levels of lead or copper present.
- Action level for lead: 0.015 mg/L (milligrams per liter)
- Action level for copper: 1.3 mg/L
Reporting of Lead and Copper Measurements
Drinking Water Watch can report a summary of lead and copper measurements for the water system, or a detailed report on samples
When you specify a water system by name, ID, or location and choose "Search For Water Systems", you can view lead and copper summary results for the system you select. The number of samples taken and the measured 90th percentile value of lead and copper are shown in the "Measure" column. These should not exceed their respective action levels.
You can discover more detailed reporting of lead and copper measures when you specify a water system by name, ID, or location and also select a sample class of "Lead and Copper Summaries". Choosing "Search For Samples" instead of "Search for Water Systems". For both lead and copper, three items are shown:
- The total number of samples taken, and the 90th percentile measure. This measure should be below the action level.
- The total number of samples taken, and the 95th percentile measure.
- The number samples that exceeded the action level.
In the example below, 10 samples were taken with a 90thmeasure for copper of 0.613 mg/L. The 95th percentile measure was 0.713, and 0 samples exceeded the action level