Decifering the Annual Water Quality Report

Yesterday, we looked at the intent and the sad fate of the Annual Water Quality Report. Today, we’re going to try to “decode” the AWQR, to see if we can actually determine if our water is safe or not. Again, I will be using the AWQR from the Castaic Lake Water Agency at www.clwa.org as my example but, because of regulations, you should find all AWQR’s to be about the same.
The first thing to recognize is the massive table of water quality data. The table should actually be much more massive, because hundreds of additional “parameters” are analyzed. Note: “parameter” is water quality-speak for anything in the water that’s not water. So, why aren’t all these other test results shown? The rules of the AWQR say that the water agency needs to show only those parameters that had positive results. Perhaps the most important message of the AWQR is that, after analyzing for a few hundred parameters, only 34 (at CLWA) were found at all — none of these other tests showed any trace of those other 200+ parameters. That’s excellent news, and it is absolutely lost on even the most intelligent and informed consumers!
So this explains the first column: any parameter in the water that had a positive result shows up here.
How about the first row of the table? In CLWA’s case, their report covers eight separate categories: one column reports on the output of their two treatment plants, and the other seven are for distinct service areas. A customer really is only concerned about his/her water, and so only needs to look at the column that shows his/her service area.
Next, within each service area column, there are three sub-columns, labeled “Minimum,” “Maximum,” and “Typical.” While the first two are pretty obvious, what the heck does “Typical” mean? Again, we engage here in WQ-speak: “Typical” really just means average. However, it is statistically difficult to average some of the water quality values, because they are not numbers. But once we get past this, read “average” instead of “typical, and you’ll do fine.
What do I mean when I say that some of the WQ values are not numbers? As we look at the table, the most common entry is less than the “DLR.” We blogged about this last December, so just look through the archives if you want a little more information on this topic. But to simplify this for the reader of the AWQR, read each “DLR” as “zero.” In short, the tests found nothing when looking for that particular parameter.
The next thing the consumer should do is compare the minimum, maximum, and typical values for each parameter against the “MCL” value. This is the Maximum Contaminant Level, and it is the official safe level for that parameter. If your actual values are less than the MCL, then your drinking water is safe, according to the best science available today.
Are you still intimidated by the AWQR table? Don’t feel alone! And just think of the poor consumer that’s trying to answer the very simple question, “Is my water safe?” Answering this question is the stated objective of the AWQR. Does this report achieve that objective?

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