3. Water Quality Index (WQI)
Drinking water to compute the WQI of USEPA and WHO recommend WQM parameters concerning different living conditions around the globe (Kashid et al. 
; Chowdury et al. 
; Kumar et al. 
; Kawarkhe et al. 
; Prasad et al. 
). WQI parameters show that measuring water quality by traditional laboratory-based methods is commonly utilized.
Total coliform (TC): In soil, human and animal waste, etc., bacteria are usually present. Generally, humans and animal feces contain a class of TC belonging to the fecal coliforms. TC measuring methods commonly use minimal medium ONPG and multiple tube fermentation, numbering the most probable membrane filtration. Organisms/100 mL is its unit. The disease-causing pathogen is a signal to humans, but its presence in Coliform bacteria is usually harmless. Gastrointestinal upset and general flu-type symptoms (e.g., abdominal cramps, fever, and diarrhea) are commonly observed symptoms.
Fecal coliform (FC): Of total coliform, it is a subdivision. Escherichia coli (E-Coli) is the most common member. In humans and animals both warm and cold-blooded, bacteria exist in waste and intestines. Other pathogenic organisms may exist, but FC are not pathogenic by themselves. ONPG is a common method of measuring FC, recording the most probable number, membrane filtration, multiple tube fermentation, and minimal medium. Organisms per 100 mL number are its measuring unit.
Total dissolved solids (TDS): Magnesium, calcium, sodium, potassium cations, etc., present in the water represent soluble solids both organic and inorganic. A minimum threshold, if it increases, becomes saline beyond salinity because the water is highly correlated. Fertilizers, pesticides, sewage treatment, floodwater, etc., are the major sources. To measure it in mg/L, the gravimetric method is generally used.
Total suspended solids (TSS): In water, both organic and inorganic material suspended represents the number of remains. Light absorption is correlated. Let water absorbs less oxygen, and more light absorption may increase TSS. This may have adverse effects on aquatic life. In mg/L to measure it is generally utilized the gravimetric scheme.
Total solids (TS): Suspended solids represent the total amount of solids when water is dissolved. Sulfur, calcium, phosphorous, nitrate, iron, etc., are generally dissolved solids. Plankton, algae, silt, clay particles, etc., may be included. The aquatic plant process affects photosynthesis in turn; the passage of sunlight through water can affect water clarity. Retaining more heat may adversely affect aquatic life, and water will heat up due to this.
Total hardness (TH): For domestic or industrial applications, TH determines the suitability of water. In water, the presence of magnesium and calcium is the concentration. With an EDTA solution, it is generally measured using a titration method. In mg/L or parts per million (PPM), calcium carbonate (CaCO3) hardness is given in terms of equivalent quantity. Magnesium and calcium are basic hard water minerals that can fulfill dietary needs, that may be beneficial for humans but are not harmful. The heated formation of calcium carbonate is the major drawback of hard water, leaving decay deposits on heating elements and pipes.
Dissolved oxygen (DO): In water, oxygen solubility is represented by DO gained from the atmosphere during photosynthesis or absorbed generally from the water. For aquatic life, it plays an essential role. It corrodes water pipes, but it may make water taste better for drinking. It is highly important for aquatic life. For example, aquatic life undergoes stress when its level falls below 5 mg/L. An electric meter or Winkler titration is generally utilized for measurement purposes.
Electrical conductivity (EC): EC represents water’s ability to conduct electric current. Water’s ionic content helps with measuring alkalinity, hardness, and some dissolved solids, though it is not involved directly. Measurement methods utilized are specifically electrical.
Chloride (Cl): Water is measured using the mg/L titration method (milligram per liter is naturally available). If 250 mg/L is a minimum threshold, exceeding it may make water taste saltier though the excess may not damage humans. For agricultural activities, excessive Cl may be harmful. Due to corrosiveness, the electrical conductivity of water increases, reacting due to soluble salts forming with metal ions in metallic pipes. This also raises the level of metals in water.
Temperature (T): T affects the chemistry of water. It increases at higher temperatures because of chemical reactions. At higher temperatures, groundwater especially can dissolve more minerals from rocks surrounding the water. Electrical conductivity will increase due to this act. Rates of gas transfer affect dissolved oxygen and have a great effect on aquatic life. It is often measured in Celsius.
Potential of hydrogen (pH): Normal water has a pH of 7. Alkalinity means a range from 8 to 14, while acidity indicates a value from 0 to 6. For humans, water with pH values from 6.5 to 8.5 is generally safe to drink 
. Electrodes and electrometry are measured using pH. If corrosive and soft, then the water is acidic.
Oxidation-reduction potential (ORP): Also known as REDOX, it is a millivolt (mV) measurement to determine either reduction or oxidization substance capability. To measure ORP, an ORP meter is used. A positive reading means the substance is an oxidizer (i.e., acceptor of electrons). A negative reading means a reducer (i.e., donor of electrons). A high ORP generally having chlorine, it is added to water to kill unwanted bacteria and pathogens. Bacteria’s DNA, and proteins from cell membrane oxidation, will attract electrons. In addition, it can disinfect water oxygen, which also has high ORP.
Total chlorine (T-Cl): This represents the levels of free and combined chlorine. To measure free chlorine and maintain residual levels, it is necessary to add appropriate solutions. To kill harmful microorganisms (e.g., viruses and bacteria), numerous municipalities intentionally add chlorine to water which, if ingested, could make us sick.
Free chlorine (F-Cl): Residual, chlorine residual, or residual chlorine is well known. Water level potability is indicated. As a dissolved gas, (Cl2), hypochlorite ion (OCl−), and/or hypochlorous acid (HOCl) is the amount of residual chlorine (RC) present in the water. A test kit can measure the total amount of Cl2, OCL, and HOCL. The measurement unit is mg/L. It is generally used to disinfect contaminated water. In digital water colorimeters or color-wheel test kits, F-Cl is tested via pool test kits. Free from recontamination during storage and most disease-causing pathogens means water is protected from its presence.