E. Coli Bacteria
Escherichia coli are a large and diverse group of bacteria. Although most strains of E. coli are harmless, others can make you sick. Some kinds of E. coli can cause diarrhea, while others cause urinary tract infections, respiratory illness and pneumonia, and other illnesses. Still other kinds of E. coli are used as markers for water contamination (Source: CDC.gov).

Total Coliform Bacteria
Coliform bacteria are microbes found in the digestive systems of warm-blooded animals, in soil, on plants, and in surface water. These microbes typically do not make you sick; however, because microbes that do cause disease are hard to test for in the water, “total coliforms” are tested instead. If the total coliform count is high, then it is very possible that harmful germs like viruses, bacteria, and parasites might also be found in the water (Source: CDC.gov).

pH
The pH level tells you how acidic or basic your water is. The pH level of the water can change how your water looks and tastes. If the pH of your water is too low or too high, it could damage your pipes, cause heavy metals like lead to leak out of the pipes into the water, and eventually make you sick (Source: CDC.gov).

Hardness (Hard Water)
Water hardness is the amount of dissolved calcium and magnesium in the water. Hard water is high in dissolved minerals, largely calcium and magnesium. Depending on the hardness of your water, after using soap to wash you may have felt like there was a film of residue left on your hands. In hard water, soap reacts with the calcium (which is relatively high in hard water) to form "soap scum" (Source: USGS.gov).

Nitrate
Nitrate is naturally found in many types of food. However, high levels of nitrate in drinking water can make people sick. Nitrate in your well water can come from animal waste, private septic systems, wastewater, flooded sewers, polluted storm water runoff, fertilizers, agricultural runoff, and decaying plants. High levels of nitrate or nitrite can decrease the ability of your blood to carry oxygen to your tissues. Infants younger than 6 months may be particularly at risk. Related symptoms can include decreases in blood pressure, increased heart rate, headaches, stomach cramps, and vomiting (Source: CDC.gov).

Lead
Lead is a toxic metal that is persistent in the environment and can accumulate in the body over time. Risk will vary depending on the individual, the chemical conditions of the water, and the amount consumed. Lead can enter drinking water when a chemical reaction occurs in plumbing materials that contain lead. This is known as corrosion – dissolving or wearing away of metal from the pipes and fixtures. This reaction is more severe when water has high acidity or low mineral content. You cannot see, taste, or smell lead in drinking water (Source: CDC.gov).

Volatile Organic Compounds (VOCs)
VOCs are industrial and fuel-related chemicals that may cause bad health effects at certain levels. Which VOCs to test for depends on where you live. Contact your local health or environmental department, or the EPA to find out if any VOCs are a problem in your region (Source: CDC.gov)

Copper
Copper (Cu) is an element and metal. It is essential for people to ingest small amounts of copper everyday in food and water. Ingesting too much or too little copper can lead to illness and/or disease. Ingesting a high amount of copper, usually in drinking water, can cause vomiting, nausea, abdominal pain, and/or diarrhea. Ingesting higher than recommended amounts of copper every day over time, such as in water can lead to severe illness, such as kidney and liver damage (Source: CDC.gov).

Iron
Iron is mainly present in water in two forms: either the soluble ferrous iron or the insoluble ferric iron. Water containing ferrous iron is clear and colorless because the iron is completely dissolved. When exposed to air in the pressure tank or atmosphere, the water turns cloudy and a reddish brown substance begins to form. Iron is not hazardous to health, but it is considered a secondary or aesthetic contaminant (Source: CDC.gov).

Manganese
Manganese is a naturally occurring substance found in many types of rocks and soil. Well water may sometimes be contaminated with sufficiently high levels of manganese to create a potential health hazard. Illnesses involving the kidneys and urinary tract have been observed in laboratory rats fed very high levels of manganese. These illnesses included inflammation of the kidneys and kidney stone formation (Source: CDC.gov).

MBAS
The MBAS (methylene blue active substances) index is an analytical convention (a method-defined parameter) used for water quality control purposes. It measures surfactants (detergent and foaming agents) and other substances that react with methylene blue under specified conditions (Source: ISO.org).

Chloride & Chlorine
Chlorination is the process of adding chlorine to drinking water to kill parasites, bacteria, and viruses. Different processes can be used to achieve safe levels of chlorine in drinking water (Source: CDC.gov) The presence of chlorine in the water sample will result in the sample to be rejected for analysis by the lab.
 
Radon (as pertaining to water)
Radon is an odorless, colorless, tasteless, naturally-occurring radioactive gas formed from the breakdown of uranium and thorium. Exposure to high levels results in an increased risk of lung cancer. Showering, washing dishes, and doing laundry can disturb the water and release radon gas into the air you breathe (Source: CDC.gov).

Turbidity
Turbidity is the measure of relative clarity of a liquid. It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample. Excessive turbidity, or cloudiness, in drinking water is aesthetically unappealing, and may also represent a health concern. Turbidity can provide food and shelter for pathogens. If not removed, the causes of high turbidity can promote regrowth of pathogens in the water. (Source: USGS.gov)

Odor

• Chlorinous, Bleachy, Chemical, or Medicinal Taste/Odor:
  aused by the addition of chlorine to the water or interaction of that chlorine with a build-up of organic material in your plumbing system. C

• Sulfurous, Decayed, or Sewage-like Taste/Odor:
  There are two common causes of a sulfurous, decayed, or sewage-like taste or odor in the water: which are bacteria growing in your drain, or bacteria growing in your water heater.

• Musty, Moldy, Earthy, Grassy or Fishy Taste/Odor:
  There are two common causes of this kind of odor in the water: which are bacteria growing in your drain, or certain types of organisms growing in the public water supply.

• Petroleum, Gasoline, Turpentine, Fuel-like or Solvent-like Odor: Although this problem is rare, it is potentially serious. It is possible that a leaking underground storage tank is near your well. Do not use the water (Source: Mass.gov)

Color
Color in drinking water can be caused by dissolved and suspended materials, and a brown shade in water often comes from rust in the water pipes. Color in water you see around you can be imparted in two ways: dissolved and suspended components. An example of dissolved substances is tannin, which is caused by organic matter coming from leaves, roots, and plant remains (Source: USGS.gov).

Total Solids (TDS)
Total solids are dissolved solids plus suspended and settleable solids in water. Higher concentrations of suspended solids can serve as carriers of toxics, which readily cling to suspended particles. A high concentration of total solids will make drinking water unpalatable and might have an adverse effect on people who are not used to drinking such water (Source: Archive.EPA.gov). 

Kerosene (Fuel Oil #1)
If fuel oils have leaked from underground storage tanks and entered underground water, you may drink contaminated water from a well containing fuel oils. Drinking kerosene may cause vomiting, diarrhea, swelling of the stomach, stomach cramps, coughing, drowsiness, restlessness, irritability, and unconsciousness; also, it may be difficult to breathe, and breathing may be painful (Source: CDC.gov)

Diesel (Fuel Oil#2)
If fuel oils have leaked from underground storage tanks and entered underground water, you may drink contaminated water from a well containing fuel oils. Drinking diesel may lead to nausea, vomiting and abdominal pain. In serious cases damage to the digestive tract, coma, loss of muscle control, and heart and lung problems can occur (Source: Gov.uk)

Lubricating/Lubricant Oil (Fuel Oil #3)
If fuel oils have leaked from underground storage tanks and entered underground water, you may drink contaminated water from a well containing fuel oils. Petroleum oils are known carcinogens, and medical records indicate that they cause uncomfortable eczema and oil acne (Source: NIH.gov)
 
Used Motor Oil
Used motor oil has contaminants that are not present in new motor oil. When a car is running, motor oil is exposed to high heat, which creates new chemicals that can be more toxic than the oil itself. Ingestion can lead to diarrhea or vomiting. vomiting of used motor oil may lead to aspiration and infection (Source: Poison.org).

Unleaded Gas
When gasoline seeps into soil it can contaminate groundwater used for drinking. Most chemicals in gasoline are removed during water treatment, but people who drink untreated water or water from private wells can be exposed. Gasoline also can be absorbed through skin during contact. Symptoms from swallowing small amounts of gasoline include mouth, throat and stomach irritation, nausea, vomiting, dizziness and headaches. Swallowing gasoline causes many accidental poisonings each year. Some effects of skin contact with gasoline include rashes, redness and swelling (Source: Idph.state.il.us).