Non-Detect (ND) measurements occur when an analytical sample has a concentration deemed to be lower than what can be detected using the method employed by the laboratory. This implies that the concentration is below the minimum detection limit of the methodology. E.g. ND (10ppm) simply means that the concentration is below the detection limit of 10 ppm.

Total Dissolved Solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. TDS are often measured in parts per million (ppm). Although TDS is not generally considered a primary pollutant (e.g. it is not deemed to be associated with health effects), it is used as an indication of aesthetic characteristics of drinking water and as an aggregate indicator of the presence of a broad array of chemical contaminants. The United States Environmental Protection Agency has established a secondary water quality standard of 500 mg/L to provide for palatability of drinking water. The most common chemical constituent are calcium, phosphates, nitrates, sodium, potassium, and chloride. The chemicals may be cations, anions, molecules. Certain naturally occurring total dissolved solids arise from the weathering and dissolution of rocks and soils. TDS is often measured in parts per million (ppm) or mg/liter.

pH is a measure of how acidic or basic a solution is.  pH is defined as the negative logarithm of the hydrogen-ion concentration and is represented on a scale typically from 0 to 14.  Solutions with a pH less than 7 are acidic, and solutions with a pH greater than 7 are basic. Solutions with a pH of 7 at 25 °C are neutral (i.e. pure water).  The United States Environmental Protection Agency has established a secondary water quality standard of between 6.5 and 8.5 for palatability of drinking water.

Calcium is an alkaline earth metal and is primarily a measure of water hardness. Water hardness is determined by the concentration of dissolved calcium and magnesium in the water. U.S. Environmental Protection Agency (EPA) has not set a legal limit or standard for hardness in water. This is primarily because the constituents that contribute to hardness (generally calcium and magnesium ions) are not toxic; that is, they do not cause harmful health effects. TDS is often measured in parts per million (ppm) or mg/liter.