Each year, the District collects groundwater samples from at least eight water wells across our service area—typically two wells per county—and submits those samples for chemical analysis focused on constituents of concern. We try to space sampling locations out as evenly as possible across the District so we’re not over-representing one area and missing another. While eight samples is our standard baseline, we can collect additional samples when a landowner has a specific need and the District can use the data based on the well’s location (for example, to fill a gap in coverage or help evaluate a local concern). Results from each year’s sampling are summarized in a water quality results table in our Annual Report to the Board of Directors, along with a clear discussion of whether any potential groundwater contamination or other issues of concern were identified in the analyses.

Each water quality sample we collect is run through a General Water Quality Test at a San Antonio TCEQ NELAP Accredited Laboratory. This means we’re looking at a broad mix of constituents that help us understand overall groundwater quality—not just one “contaminant.” As shown in the chart on the right, the lab analyzes general chemistry to include: alkalinity, conductivity, total dissolved solids (TDS) and pH. Temperature of the sample is taken at the well site location and again at the lab, the samples are immediately placed on ice once sampled from the wells, so the lab temperatures are not representative of the aquifer temperatures. Key anions tested include: fluoride, chloride, nitrate, and sulfate. Common metals tested include: aluminum, arsenic, calcium, copper, iron, lead, magnesium,  manganese, sodium, and zinc.

This gives us a well-rounded snapshot of what’s in the groundwater and helps us spot patterns, changes, or outliers over time and across the District.

On the chart, MCL stands for Maximum Contaminant Level, which is the “do not exceed” numbers used for drinking water standards set by the EPA—if a result is over the MCL, it’s a sign that the water may need a closer look, follow-up sampling, or treatment depending on the situation.

You’ll also see NSE, which stands for No Standard Established. That doesn’t mean the constituent is “bad” or “good”—it just means there is not a set regulatory limit listed for that constituent, so we interpret it using trends, typical ranges for the area, and the overall chemistry of the sample.