SVL supplies a Cation/Anion (C/A) Balance as part of our routine report when certain cations and anions are requested. Cations are the positively charged species, and anions are the negatively charged species. In a perfectly balanced sample of water, the milli-equivalent (meq) ratio of Cations to Anions is 1.00. This is referred to as the C/A balance. For many samples—especially those that are complex, acidic, or contain sediment and solids—the C/A balance is often skewed with either cation or anions being significantly higher or lower than the other. In order to calculate a C/A balance, the following analytes must be analyzed: Ca, K, Mg, Na, alkalinity, Cl, and SO4. These represent the major cations and anions in a typical sample. There are other cations and anions that can also contribute to the C/A balance such as other metals, F, and NO3. High levels of NO3 and P often give rise to poor C/A balances. Many clients submit metals (cations) as “dissolved” (filtered) and a raw unfiltered bottle for anions. We often see less than optimal C/A balances for a filtered vs. non filtered analytes. Another interesting thing to check is Total Dissolved Solids (TDS). The total for the concentrations of cations and anions (mg/L) should add up to the TDS value in mg/L.