What Terms are Associated with Water?

Water, nature's most abundant resource, comes in many forms from many places. What types of water are out there? How do we know what sort of water we’re even dealing with? Read on to find out more about this seemingly plain liquid that has a whole lot more going on than you may think.

Common Water Quality Parameters

What makes one sample of water different from another? How do we tell if a random sample of water came from a hose, pond, well, or city water source? How clean is that water? We can determine all these things by testing the water for several parameters ranging from the basic parameters listed below, to a full spectrum analysis of the water detailing everything it contains on a molecular level. Rarely is that level of testing used as we can determine a lot about a particular water sample using the below parameters through surprisingly affordable lab testing and field instruments.

Temperature: Pretty straightforward parameter, simply the temperature of the water. Why is water temperature important? The temperature of the water in question will affect other parameters such as pH, Conductivity, TDS/Salinity, and Dissolved Oxygen (DO).

pH: What exactly is pH? The simple answer is pH is the measure of how acidic or basic water is on a scale of 0 to 14. A pH of 7 is considered neutral, above 7 is basic (alkaline) and below 7 is acidic. In the case of freshwater pH is typically around 7, leaning slightly acidic or basic depending on what minerals or contaminants are in the water. Seawater is closer to a pH of 8. The pH of the water is important because it affects what minerals or nutrients may or may not be available to the ecosystem. Extreme pH levels are not only unhealthy for living organisms but can also cause damage to equipment. Extremely low pH levels can dissolve metals like piping and overly high pH can lead to mineral deposits and scale encrusting your piping. The pH value is based on the concentration of hydrogen ions in a water-based solution measured in moles per liter.

ORP/Redox: What does ORP mean? ORP, or Oxidation Reduction Potential (sometimes referred to as Redox) is a measure of how oxidizing or reducing something is to another object or substance. For example, waters potential to oxidize metal can be measured in ORP. ORP is typically measured on a millivolt scale using a platinum electrode with positive readings being oxidizing and negative readings being reduced. Both are measures of a substance's number of electrons, or more specifically electron imbalance. If something has fewer electrons than it needs it is considered oxidizing and will try to take electrons away from something else through the process of oxidation. On the flip side, if electrons happen to have a surplus of ions they will be able to give some of those electrons up without losing stability themselves. These substances are considered reducing, or antioxidizing substances. Antioxidants are just that, substances that are able to give up their free electrons to oxidation while remaining stable. A good example of helpful ORP measurement would be a swimming pools chlorination system. An ORP meter will keep track of the desired level of oxidation needed to control bacteria in the pool and dose chlorine as needed to keep those levels up.

Conductivity: What is Conductivity? Conductivity is simply a measurement of how electrically conductive something is, in this case, water. Also referred to as EC (Electrical Conductivity) or Specific Conductance (a conductivity reading referenced to a specific temperature value). Conductivity is a widely used water quality parameter and is measured with a series of electrodes applying a voltage to the sample to measure how well it conducts from pole to pole. There are many different styles of conductivity sensors out there geared towards different applications, but their core principle is the same. Conductivity is typically measured on a Siemens scale and is referenced to a volume, commonly micro-Siemens per centimeter or uS/cm when dealing with water. Pure H2O is not very conductive at all, measuring near 0 on the uS/cm scale. As the water absorbs minerals, salts, and other impurities into solution it becomes more electrically conductive. For example, freshwater can range from the low 100’s to 1000’s of uS/cm depending on mineral content where Seawater will range from 40,000 to 80,000+ uS/cm due to the high salt content (Salt is a great conductor). Conductivity will also vary due to temperature, for this reason many choose to reference their conductivity readings to a standard lab reference temperature such as 25 Degrees Celsius. This removes temperature as a variable in conductivity readings so we can track actual changes in concentration in the water. Concentration of what exactly will depend specifically on the type of water being tested. Conductivity is a base value for measuring TDS and Salinity in the field as well.

Total Dissolved Solids (TDS): What are Total Dissolved Solids? Total Dissolved Solids, or TDS, are minerals, salts, and other solid materials that have been dissolved into water. As rainfall travels to its final destination, it slowly dissolves and absorbs parts of the landscape along the way. The types of rock, soil and vegetation the water travels through will determine whether it ends up being “soft” or “hard”. Water flowing through soft rock such as limestone will absorb calcium and magnesium fairly quickly making it hard water (high mineral content), where water flowing through hard rock such as granite will end up being soft water (low mineral content). TDS is calculated based on the waters conductivity and known mineral content. For example, when dealing with fresh water the average conversion factor for TDS is a multiplier of 0.49 (roughly half the conductivity value) when measured in uS/cm. More specific conversion factors can be calculated for specific bodies of water by analyzing that specific body of waters exact chemical make-up. By measuring TDS we can monitor the amount of “stuff” dissolved in the water of interest and by doing so track any sort of contamination (a spike in TDS readings) or dilution (influx of fresh, clean water) that the body of water may experience. For example, by monitoring the TDS of stormwater entering a lake you can estimate the amount of contaminants entering the lake's ecosystem from that rain event.

Salinity: What is Salinity? Salinity is a measure of how saline, or salty, a particular body of water is. Salinity measurements are used to measure the salt content of water to determine whether it is fresh or saltwater, with brackish water falling in between the two (a combination of salt and fresh water such as the water found where a river meets the sea). Salinity is another measurement that is based on the waters conductivity value and takes into account the temperature and pressure (depth) the reading was taken at for accuracy. Salinity is a key parameter when monitoring the health of a saltwater ecosystem, certain plants and animals require very specific salinity levels to stay healthy.

Total Suspended Solids (TSS): What is TSS? TSS, or Total Suspended Solids, are a measurement of solid particles within a sample of water. Unlike TDS, which is dissolved into solution with the water, TSS quantifies the tiny solid particles found within the water. These particles could be dirt, sediment, algae, plastics, or any tiny solid that doesn’t dissolve into the water. Some TSS may settle out to the bottom of a container while others remain partially suspended within the water column but in either case, they count towards the TSS measurement. TSS levels are typically obtained by lab analysis by taking a known water sample weight, removing said water by filtration or evaporation, then weighing the remaining solids. From there the solids can be further analyzed to determine their type or source of contamination or considering natural material be used to help predict future silt accumulation in a river ecosystem.

Turbidity: What is Turbidity? Turbidity is the measurement of the clarity (or cloudiness) of water. Unlike TSS, Turbidity is measured by the water's clarity so although TSS may contribute to the Turbidity of a water sample not all Turbidity is a suspended solid. Turbidity is measured by applying a specific amount and frequency of light and measuring how much light scatters back to receiving sensor and typically recorded in units of NTU (Nephelometric Turbidity Unit). Along with suspended solids, dyes, colored or florescent organic material, and tannins can increase turbidity levels. Perfectly clear water reads 0 on the NTU scale, at 20 NTU a slight haze to the water can be noticed. When the turbidity reaches 100 NTU it will appear cloudy and at 800 NTU begin to appear like skim milk or strong tea depending on the source of coloration. Although Turbidity doesn’t equal TSS it is often used to estimate the amount of solids contained in the water in continuous monitoring applications.

Dissolved Oxygen: What makes dissolved oxygen important? The amount of oxygen dissolved (or DO) in water is crucial to aquatic life making DO levels in streams, rivers, and lakes critical to fishery health. On the other hand, even small amounts of DO in a steam boiler system will rapidly damage critical components. Dissolved oxygen is measured through various methods such as fluorescence quenching optical sensors or membrane-based galvanic sensors and are expressed in units of volume such as mg/L or a percent of saturation (referenced to air or water). Dissolved oxygen plays a key role in water quality.

Alkalinity; What is Alkalinity? Alkalinity is a measurement of water's resistance to becoming acidified. Related to pH but not directly, Alkalinity represents the waters' ability to resist shifting from basic to acidic pH levels (otherwise known as its buffer capacity). This means water with high alkalinity will take more of an acidic material to turn it acidic than water with low alkalinity. You’ll often come across alkalinity when maintaining a swimming pool. Keeping alkalinity levels high is important to maintaining stable pH and free chlorine levels.