Water Quality Characteristic :Physical - Chemical-Biological
1.Temperature
a.Water temperatureis a controlling factor for aquatic life.
b.It controls the metabolic rates of aquatic organism; the rate of photosynthesis by aquatic plants; reproductive activities and therefore, life cycles; and also the sensitivity of organisms to toxic wastes, parasites, and diseases.
c.Water temperature is influenced by the quantity and velocity of stream flow. The sun has much less effect in warming the waters of streams with greater and swifter flows than of streams with smaller, slower flows.
d.Temperature will affects the concentration of dissolved oxygen in water.
e.Oxygen is more easily dissolved in cold water. On the other hand, we can say that oxygen levels become lower as temperature increase.
f.The temperature of a water supply will influence on how it tastes, how easily it dissolves impurities, how effective it is for other uses such as cooling.
2.pH
a.pH is a term used to indicate the alkalinity or acidity of a substance as ranked on a scale from 1.0 to 14.0.
b.pHis an important limiting chemical factor for aquatic life.
c.If the water in a stream is too acidic or basic, the H+ or OH- ion activity may disrupt aquatic organism’s biochemical reactions by either harming or killing the stream organisms.
d.The following pH scale shows relative pH ranges that support aquatic life. At either very high or low pH, the water cannot support most organisms.
e.pH is an important factor in the chemical and biological systems of natural waters. The toxicity of many compounds is affected by pH.
f.One example is hydrogen cyanide (HCN). Cyanide toxicity to fish increases as the pH is lowered.
g.The solubility of metal compounds contained in bottom sediments or as suspended material also is affected by pH.
h.As pH decreases, certain metals such as aluminium copper, and lead are more easily dissolved and are leached from soil and sediments into runoff and groundwater entering surface water. These metals can accumulate on fish gills or cause deformities in fish fry, reducing their chance to survive.
3.Turbidity
a.Turbidity is a measure of water clarity which is how much the material suspended in water decreases the passage of light through the water.
b.Suspended materials include soil particles (clay, silt, and sand), algae, plankton, microbes, and other substances. These materials are typically in the size range of 0.004 mm (clay) to 1.0 mm (sand).
c.Turbidity can affect the colour of the water.
d.Low levels of turbidity may indicate a healthy, well-functioning ecosystem, with moderate amounts of plankton present to fuel the fuel the food chain.
e.However, higher levels of turbidity pose several problems for stream systems.
f.Turbidity blocks out the light needed by submerged aquatic vegetation.
g.It also can raise surface water temperatures above normal because suspended particles near the surface facilitate the absorption of heat from sunlight.
4.Total Suspended Solid
a.Total solids are dissolved solids plus suspended and settleable solids in water.
b.In stream water, dissolved solids consist of calcium, chlorides, nitrate, phosphorus, iron, sulphur, and other ions particles that will pass through a filter with pores of around 2 microns (0.002 cm) in size.
c.Suspended solids include silt and clay particles, plankton, algae, fine organic debris, and other particulate matter. These are particles that will not pass through a 2-micron filter.
d.The concentration of total dissolved solids affects the water balance in the cells of aquatic organisms.
e.An organism placed in water with a very low level of solids, such as distilled water, will swell up because water will tend to move into its cells, which have a higher concentration of solids.
f.An organism placed in water with a high concentration of solids will shrink somewhat because the water in its cells will tend to move out.
g.This will in turn affect the organism's ability to maintain the proper cell density, making it difficult to keep its position in the water column. It might float up or sink down to a depth to which it is not adapted, and it might not survive.
h.Total solids also affect water clarity.
i.Higher solids decrease the passage of light through water, thereby slowing photosynthesis by aquatic plants.
j.Water will heat up more rapidly and hold more heat; this, in turn, might adversely affect aquatic life that has adapted to a lower temperature regime.
k.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.
l.Levels of total solids that are too high or too low can also reduce the efficiency of wastewater treatment plants, as well as the operation of industrial processes that use raw water.
5.Taste, Colour, Odor
Colour
- Although colour in raw water can be present in groundwater due to certain minerals, it is primarily a concern for surface water sources. This is due to the decomposition of organic material.
Taste and Odour
- Taste and odour in water can be due to factors such as chemicals, minerals, decaying organic matter, and dissolved gases.
- The most common causes of odour in drinking water are the presence of hydrogen sulphide, iron, or sulphur-reducing bacteria.
- Even though taste and odour are considered more of an aesthetic concern, they can also indicate the presence of contaminants that are harmful to a person's health.
6.DO
- The amount of dissolved oxygen (DO)in water is expressed as a concentration.
- A concentration is the amount in weight of a particular substance per a given volume of liquid.
- The DO concentration in a stream is the mass of the oxygen gas present.
- It is measured in milligrams per liter (mg/l) or parts per million (ppm).
The concentration of dissolved oxygen in a stream is affected by many factors:
a.Temperature: Oxygen is more easily dissolved in cold water.
b.Flow: Oxygen concentrations vary with the volume and velocity of water flowing in a stream. Faster flowing water tend to be more oxygen rich because more oxygen enters the water from the atmosphere in those areas than in slower, stagnant areas
c.Aquatic Plants: The presence of aquatic plants in a stream affects the dissolved oxygen concentration. Green plants release oxygen into the water during photosynthesis. Photosynthesis occurs during the day when the sun is out and ceases at night. Thus in streams with significant populations of algae and other aquatic plants, the dissolved oxygen concentration may fluctuated daily, reaching its highest levels in the late afternoon.
d.Altitude: Oxygen in more easily dissolved into water at low altitudes that at high altitudes.
e.Dissolved or suspended solids: Oxygen is also more easily dissolved into water with low levels of dissolved or suspended solids.
7.BOD
- The Biological Oxygen Demand (BOD) is the amount of oxygen consumed by bacteria in the decomposition of organic material.
- It also includes the oxygen required for the oxidation of various chemical in the water, such as sulfides, ferrous iron and ammonia.
- BOD measures the oxygen consumed by microorganisms as they decompose organic matter and includes any chemical oxidation of inorganic compounds.
- BOD is determined by measuring the dissolved oxygen level in a freshly collected sample and comparing it to the dissolved oxygen level in a sample that was collected at the same time but incubated under specific conditions for a certain number of days (usually five days).
- The difference in the oxygen readings between the two samples in the BOD is recorded in units of mg/L.
- Unpolluted; natural waters should have a BOD of 5 mg/L or less. Raw sewage may have BOD levels ranging from 150 – 300 mg/L
- The measurement of oxygen demand is an easy way to detect the degree of pollution by organic matter.
- High BOD values in a stream usually indicate a source of wastewater that shouldn’t be there (high degree of pollution).
- Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water.
8.COD
- Chemical oxygen demand (COD), is similar in function to BOD in that both measure the amount of organic compounds in water.
- However, COD is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biologically active organic matter.
- COD values are always greater than BOD values, but COD measurements can be made in a few hours while BOD measurements take five days.
9.Phosphorus
- Phosphorus is often the limiting nutrient for plant growth, meaning that it is in short supply relative to nitrogen.
- Phosphorus usually occurs in nature as phosphate, which is a phosphorous atom combined with four oxygen atoms (PO4-3).
- Phosphate that is bound to plant or animal tissue is known as organic phosphate. Phosphate that is not associated with organic material is known as inorganic phosphate.
- Both forms are present in aquatic systems and may be either dissolved in water or suspended (attached to particles in the water column).
- Phosphorus is an essential element for plant life, but when there is too much of it in water, it can speed up eutrophication (a reduction in dissolved oxygen in water bodies caused by an increase of mineral and organic nutrients) of rivers and lakes.
10.Nitrogen
- Nitrogen, in the forms of nitrate, nitrite, or ammonium, is a nutrient needed for plant growth. Although nitrogen is abundant naturally in the environment, it is also introduced through sewage and fertilizers.
- Chemical fertilizers or animal manure is commonly applied to crops to add nutrients.
- Heavy rains can generate runoff containing these materials into nearby streams and lakes.
- Wastewater-treatment facilities that do not specifically remove nitrogen can also lead to excess levels of nitrogen in surface or ground water.
- Excess nitrogen can cause over stimulation of growth of aquatic plants and algae. Excessive growth of these organisms, in turn, can clog water intakes, use up dissolved oxygen as they decompose, and block light to deeper waters.
- This seriously affects the respiration of fish and aquatic invertebrates, leads to a decrease in animal and plant diversity, and affects our use of the water for fishing, swimming, and boating.
- Too much nitrate in drinking water can be harmful to young infants or young livestock.
11.Biological Characteristic
- The biological characteristics of water refer to a variety of living organisms that can be found in water.
- These include microscopic viruses, bacteria and protozoan; as well as phytoplankton (microscopic algae), zooplankton (tiny water animals), insects, worms, large plants and fish.
- Waterborne pathogens are disease-causing bacteria, viruses, and protozoans that are transmitted to people when they consume untreated or inadequately treated water.
- Two protozoans in the news today are Giardia and Cryptosporidium. Their consumption can lead to severe problems of the digestive system, which can be life-threatening to the very young, very old, or those with damaged immune systems
