EVALUATION PARAMETERS for POTABLE (Drinking) WATER
PHYSICAL AND CHEMICAL PARAMETERS FOR EVALUATION OF POTABLE WATER
1.Taste
- Must have no objectionable taste
- The cause of taste must be determined
2.Odor
- Must have no objectionable odor
- The cause of odor must be determined
3.Color
a. Apparent - maximum of 10 Color Units
b. True - maximum of 5 Color Units
- Decomposition of organic materials such as leaves or woods usually yield coloring substances to water; Tannins, humic acid, and humates from the decomposition of lignin; Insoluble form of iron and manganese; colored suspended matters
- Method of test is by visual comparison or Colorimetry
4.Turbidity
- measures the light-transmitting properties of water
- maximum acceptable value: 5 NTU (Nephelometric Turbidity Unit)
- Turbidity increases with the quantity of suspended matters in water.
- Method of analysis is by Turbidimetry
5.Chemical contaminants
There are chemical constituents of water that can lead to acute health problems except through massive accidental contamination of drinking water supply. In such incidents, water usually becomes undrinkable owing to unacceptable taste, odor, and appearance.
a. Inorganic constituents
Certain inorganic constituents may be present in drinking water as a result of leaching out of piping or plumbing materials such as lead, copper, asbestos, nickel and cadmium. Some of these chemicals are known or suspected carcinogens such as arsenic, lead, chromium, and cadmium among others.
b. Organic constituents
Organic constituents in water could come from various sources such as the decomposition of organic debris, domestic, agricultural and industrial activities and contamination that occur during water treatment and distribution. These activities generate wastewater discharges, agricultural and urban runoff and leachates from contaminated soils that may include pesticides, solvents, metal degreasers and plasticizers and petroleum products. Other organic contaminants are formed during water treatment processes such as coagulation, chlorination and ozonation. Examples of organic constituents which may contaminants drinking water are DDT (dichlorodiphenyltrichloroethane), endrin, benzene carbon tetrachloride, carbofuran, vinyl chloride, toluene, PAHs (polynuclear aromatic hydrocarbons), etc.
6.pH
- Standard drinking water pH is from 6.5 to 8.5
- Standard pH of 5 – 7 for water that undergone reverse osmosis or distillation process
- The pH range is based on aesthetic consideration only. The acceptable range may be broader in the absence of a distribution system. pH is important as operational water quality parameter
- Method of analysis is by Electrometric method
7.Total Dissolved Solids (TDS)
- TDS in drinking water originate from natural sources, sewage, urban runoff and industrial wastewater.
- Maximum allowable level – 500 mg/L
- Standard TDS of <10 mg/L for water that undergone reverse osmosis or distillation process
- Method of analysis is Gravimetric method, dried at 180oC
8.Hardness
Hardness is due to the presence of naturally occurring divalent cations, such as calcium, magnesium, and strontium resulting from contact of acidic groundwater with rocks such as limestone and dolomites. Hardness beyond the standard value maybe acceptable by the consumers in certain areas.
- Maximum tolerable level: 300 mg/L as CaCO3
- Method of analysis: Flame Atomic Absorption Spectrometry (FAAS), Electrothermal Atomic Absorption Spectrometry (EAAS), Inductively Coupled Plasma (ICP), Colorimetry Method
9.Disinfectants and Disinfectant By-Products
When sufficient dosage of chlorine is applied to water, micro-organisms of sanitary significance are destroyed and all the oxidizable matter are reacted upon. After all of these reactions have taken place, at the end of a specified contact time, there remains a certain minute quantity of chlorine in the water. This is detected as residual chlorine. Its presence in water is usually an indication, and is therefore an assurance of protection of the bacteriological quality.
- Residual chlorine must be a minimum of 0.30 mg/L occurring at the farthest point of distribution system and a maximum of 1.5 mg/L detected at any point in the distribution system.
- Some chemicals might be found in drinking water as a result of disinfection, such as bromate, chlorite, chlorate, dichloroacetic acid, etc. Maximum tolerable levels of these chemicals in drinking water are listed in DOH DAO # 2007 - 0012
MICROBIOLOGICAL PARAMETERS FOR EVALUATION OF POTABLE WATER
Water used for drinking must be free from pathogenic organisms responsible for waterborne diseases. These pathogenic organisms include bacteria, viruses, protozoans and helminths.
Elimination of all these pathogenic agents from drinking water is essential for the protection of public health. Two approaches can be used to reduce the risk of bacterial,viral and parasitic infection to a negligible level: (1) providing drinking water from a source verified free of fecal contamination or (2) adequately treating fecally contaminated water.
The primary objective of bacterial examination of drinking water is the detection of fecal pollution. Although it is now possible to detect the presence of many pathogens in water, the methods of isolation and detection are often complicated and lengthy. It is therefore impossible and impractical to identify every disease causing organism present in water. The approach is to use normal enteric organisms which are the coliform group especially Escherichia coli (E. coli) as the essential indicator to fecal pollution. E. coli is a bacteria that is an indicator of whether human or animal waste has entered the water supply. These organisms are easy to detect and their presence in a sample indicates that water may be contaminated with organisms that can cause disease.
Source:
Lecture from
Introduction to Wastewater Treatment and Disposal
Lesson 3