16. Water

WATER:

• Water is essential for life; it constitutes 2/3 portion of weight.
• It is very essential for cooking, drinking & washing to promote health status.
• Chemically it is made up of oxygen and hydrogen. Its chemical formula is H20.

Safe or Wholesome Water:

• It refers the water which is tasteless, colorless, odorless, clear, transparent, free from microorganisms and does not harm the health.

Daily average requirement of water per one individual:

• Drinking =  0.5 Gallons
• Cooking = 0.5 Gallons
• Washing of Utensils = 01 Gallons
• Ablution = 01 Gallons
• Laundry = 04 Gallons
• Agriculture = 05 Gallons
• Bathing = 08 Gallons

Natural Sources of Water:

• Rain water
• Surface water
• Underground water

1. Rain Water:

• It is chief source of water
• It is sterile, clean, purest form of water & suitable for drinking.
• It is really distilled water
• The impurities collected by the rain before it reaches the surfaces. Rain takes these impurities from the air.
• Due to presence of sulfur & nitrogen oxide emitted by power plants in atmosphere which reach with rain water & forming dilute solutions of sulfuric and nitric acid and precipitation of this “ACID RAIN”, has serious effect on health & ecosystem.
• Rainfall makes acids with Aluminum, lead, zinc and iron from the soil and carries aluminum to rivers and lakes to make them polluted.
• Due to this acid rainfall, many forest-trees & marine life is being destroyed.
• The removal of hardness of rainwater makes it useful in washing and absence of lime salts makes it desirable for cooking.
• It is useful only for drinking, if individual or community, when it is collected directly from roofs of houses or in catchments.

Safe Collection of Rainwater:

• Care of collecting surface
• Separation of the first flow of rainwater, which contains most of the gross impurities.
• Location and construction of storage cistern.

2. Surface water:

• It includes rivers, creeks, lakes, streams, ponds, and man-made impounding reservoir.
• Its composition is variable & depends upon the characteristics of catchment’s basin.
• It is directly exposed to the pollution by surface wash and water carriage system.
• Most large cities depend on this water.

a. Rivers & Streams:

• Rivers and streams are the natural drainage channel of water of any region.

b. Lakes:

• These are natural and man-made, which may improve water drawn from the watersheds or catchment’s areas.
• Water remains stored for long time in lakes.
• Due to long time storage of water, it promotes sedimentation of colloid and suspended impurities in water.
• Disinfections occur due to long exposure of water to sunlight in lakes.
• Decreasing contaminants of rainstorms due to long storage.

3. Ground Water:

• It is the part of rainfall water infiltrate into the soil passes downwards through the underlying subsoil layers and rocks to various depths below the surface. Later that same water is pulled out and known as ground water.
• Rainy water goes down up to impervious stratum layer. This layer does not permit the water to go down more.
• Area above the “Impervious layer” is saturated with surface and rainy water, the area is called Saturation Zone & such water is called “Ground Water”
• Ground water is recharged with rainwater.
• Due to infiltration of rainwater down to the soil, is subjected to a natural process of purification. So, greater the distance water travels through the soil, the greater the reduction in bacterial count.
• Ground water is much better than surface water, if it is in soft form. (Water free from salts & chemicals).

Comparison between Surface & Ground Water

Nature of comparison	Surface Water	Ground Water
Availability	Stream, lakes rivers, ponds and storage reservoirs	Springs, infiltration, glaciers, shallows & deep wells
Quantity	Large during rainy season, less in summer	Small as compared to surface water
Storage	Required arrangements, for meeting demands of dry season	No storage is required; water is always available in wells & in hand-pumps
Quality	More polluted More suspended impurities Quality poor as compared to ground water May contain harmful organisms	Less polluted Less suspended particles Quality of water is better, however is usually hard water Free from organism
Treatment	Requires through treatment and constant check	May or may not required treatment
Provision	Feasible for big cities and industrial towns	Feasible for small towns, villages and individual households

Followings are resources of ground water

3.1 Springs:

• It is natural outflow of sub-surface or ground water at the earth’s surface.
• It is the groundwater.

a- Types of springs:

I- Gravity Springs:

It occurs when water-holding strata of earth are exposed in a valley against vertical cut.

II- Deep Springs:

• Can be formed when the water holding layer of earth is closed between two impervious layers and because of increased hydraulic gradient water flows out automatically.
• Relative Quality is better but quantity is low.

(Meher Hansotia p-382)

III- Springs due to fault in rock:

• These occur when the ground water rise through the fault in upper impervious layer.
• Quantity of water is large in this type of spring.

3.2 Well

The Vertical hole, dug out or drilled into the ground to get ground water is known as a Well.

a- Types of Well:

I- Shallow Well:

• Which tapes water from above the first impervious layer of earth? Water is not better for drinking & is less purified as compared to deep well’s water.
• Dried sooner than deep well.

II- Deep Well:

• Which tape the water bellow the first impervious layer of earth Quality & quantity of water is better.

III- Open Well:

• Dug up to the 30 Meters deep into soil.
• Water is taping from the sub-soil layer.
• It does not tear the impervious layer of soil.
• Quality of water is not good & limited for time.

IV- Driven Well:

• It may be deep or shallow
• Pipe is passed into soil to the level of water.
• Quantity is low but quality of water is very good
• Hand-pump is an example of this well.

V- Tube Well:

• The pipe is fitted with filter into soil, up to first impervious layer or deeper.
• Sunk into ground to tap water from underground water.
• This method is used by Municipals in small town or used by farmer for agriculture.

What are the impurities of water?

Dissolved Impurities	Suspended Impurities
Gasses e.g. CO2, H2S, NH3	Particles of sand
Industrial waste	Clay or slit
Sewage	Bacteria
Albuminoidal	Viruses
Ammonia	Fungi
Calcium Bi-Carbonate, Sulfates, Chlorides, Nitrates etc.	Ova & Larva of insects
Magnesium Carbonate, Sulfates, Chlorides & Nitrate	Insects
Iron Sulfates, Bi-Carbonates	Plants
Sodium Chlorides, Nitrate etc.	Leaves of plants
Manganese Sulfates or bi-carbonates	Algae
Cyanides, Mercury, Pesticides, etc.	Dead animals etc.

Types of Water:

Hard Water:

• Water which does not readily form the foam with soap.
• The water contains Bi-Carbonates, sulfates, Chlorides, and nitrates mainly of Magnesium, Calcium in amount of 75 or more than 75 mg per liter. E.g. Magnesium Sulfate etc…
• The term expressed the soap destroying characteristic of water.
• Unit Measuring hardness of water is milli-Equavalent per liter of water, its symbol is mEq/L

There are two types of hardness of water:

1. Temporary Hardness Water:

This is hardness of water due to presence of bi-carbonates of calcium and Magnesium (E.g. Magnesium carbonate).

• Permanent Hardness of Water:

This is hardness due to presence of sulfates, chlorides and nitrates of Calcium & Magnesium etc (E.g. Magnesium Sulfate).

• Methods of removing hardness of water:

Temporary hardness can be, removed by boiling the water or addition of lime in water. One Ounce of quick Lime per 700 gallons of water for each degree of hardness (14.25 ppm) is sufficient. Permanent & Temporary hardness can be removed by addition of Caustic Soda (Bleaching Powder).

Degrees of hardness of water:

Classification	Level of Hardness
Soft Water	Less than 1 mEq/L (1-74 mg/Liter)
Moderately Hard Water	1-30 mEq/L (75-150 mg/L)
Hard Water	30-60 mEq/L (150-300 mg/L)
Very Hard Water	More than 60 mEq/L (More than 300 mg/L)

Water Purification Methods:

Water that is distributed in cities or communities is treated extensively. Specific water purification steps are taken, in order to make the water meet current water standards. Purification methods can be divided up into settling of suspended matter, physical/chemical treatment of colloids and biological treatment. All these treatment methods have several different applications.

1. Physical water purification Methods:

Physical water purification is primarily concerned with filtration techniques. Filtration is a purification instrument to remove solids from liquids. There are several different filtration techniques. A typical filter consists of a tank, the filter media and a controller to enable backflow.

a) Screens:

Filtration through screens is usually done at the beginning of the water purification process. The shape of the screens depends on the particles that have to be removed.

b) Sand filtration:

Sand filtration is a frequently used, very robust method to remove suspended solids from water. The filter medium consists of a multiple layer of sand with a variety in size and specific gravity. When water flows through the filter, the suspended solids precipitate in the sand layers as residue and the water, which is reduced in suspended solids, flows out of the filter. When the filters are loaded with particles the flow-direction is reversed, in order to regenerate it. Smaller suspended solids have the ability to pass through a sand filter, so that secondary filtration is often required. Following two methods are used in sand filtration:

I- Slow Sand Filtration:

• Structurally and functionally it is comprised on three chambers or tanks. Each chamber’s size is 8 to 15 or depending on the amount of water needed. Below are the name and functions of tanks.

1. Settling Tank is for Storage & Sedimentation of water.

• After storage Alum (Aluminum sulfate) is added in water in amount of 01 Ounce per 180 gallons water to sediment the dissolved impurities in the bottom of tank.

2. Filtration Tank, for Filtration of suspended impurities of water.

• This chamber have three layers of Sand & gravel (mixture of coarse sand and small stones) total measuring 3 to 4.5 feet to down. & 3 to 4 feet vacuum on surface for collection of water.
• In this tank one perforated pipe is also placed on bottom to suck the filtered water & it carries to the chlorination Tank.
• Water is poured from Settling tank & the layers of sand & gravel filters the suspended impurities in water.

3. Chlorination Tank is for addition of chlorine & it disinfects the water.

II – Rapid Sand Filtration:

It is comprised on five chambers or tank or section.

1. Mixing Chamber: For Addition of Alum (Aluminum Sulfate) from chemical Tank.
2. Flocculation Chamber: For stirring with mechanical fans, mixing of Alum homogenously & Formation of Floc (Coagulated Dissolved Impurities).
3. Settling Tank: Here Heavy floc is trapped & removed, odor & color is removed & water is clarified now. Here PH of water is also maintained by adding Lime or soda bicarbonate. (Normal pH of water is 7 to 7.5).
4. Filtration Tank: Its two third (2/3) portion is filled with 03 layers of sand & gravel. These layers remove the suspended impurities from water.
5. Chlorination Chamber: Chlorine is added here, which destroy the organisms.

• Rapid sand filtration method is costly in initial but very cheap in long run.
• It takes small space for construction

Difference between Slow Sand Filtration and Rapid Sand Filtration:

S. No.	Slow Sand Filtration	Rapid Sand Filtration
1	Initial cost is low but maintenance is high	Initial cost is high but maintenance is low
2	Primary treatment is not always necessary	Primary treatment is necessary
3	Filters 2 Million gallons per day	Filters 100 to 175 Million gallons per day
4	The Chemical, Biological & Physical process is done	Chemical, Mechanical & Physical process is done
5	Reduces the organism up to 99%	Reduces the organism up to 90%
6	Vital Layer of Fungi play an important role	Residual coagulants form mechanical layer which play an important role
7	Color of water is reduced less	Color of water is reduced more

c) Cross flow filtration:

Cross flow membrane filtration removes both salts and dissolved organic matter, using a permeable membrane that only permeates the contaminants. The remaining concentrate flows along across the membrane and out of the system and permeate is removed as it flows along the other side of the membrane.

There are several different membrane filtration techniques, these are: micro filtration, ultra filtration, nano filtration and Reversed Osmosis (RO). Which one of these techniques is implemented depends upon the kind of compounds that needs to be removed and their particle size. Below, the techniques of membrane filtration are clarified.

d) Membrane Filtration Methods:

I- Microfiltration:

Microfiltration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of 0.1 to 1.5 microns, are separated from a liquid. It is capable of removing suspended solids, bacteria or other impurities. Microfiltration membranes have a nominal pore size of 0.2 microns.

II – Ultra filtration:

Ultra filtration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of 0.005 to 0.1 microns, are separated from a liquid. It is capable of removing salts, proteins and other impurities within its range. Ultra filtration membranes have a nominal pore size of 0.0025 to 0.1 microns.

III –Nano filtration:

Nano filtration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of approximately 0.0001 to 0.005 microns, are separated from a liquid. It is capable of removing viruses, pesticides and herbicides.

IV- Reversed Osmosis (RO):

Reversed Osmosis, or RO, is the finest available membrane separation technique. RO separates very fine particles or other suspended matters, with a particle size up to 0.001 microns, from a liquid. It is capable of removing metal ions and fully removing aqueous salts.

V – Cartridge filtration:

Cartridge filtration units consist of fibers. They generally operate most effectively and economically on applications having contamination levels of less than 100 ppm. For heavier contamination applications, cartridges are normally used as final polishing filters.

VI- Boiling:

Boil the water for 30 minutes. This will destroy the microorganism and remove the temporary hardness of water. This is easy, cheap and domestic method of filtration.

2. Chemical water purification Methods:

Chemical water purification is concerned with a lot of different methods. Which methods are applied depends on the kind of contamination in the (waste) water. Below, many of these chemical purification techniques are summed up.

a- Chemical addition:

• There are various situations in which chemicals are added, for instance to prevent the formation of certain reaction products. Below, a few of these additions are summed up.
  • Chelating agents are often added to water, in order to prevent negative effects of hardness, caused by the deposition of calcium and magnesium.
  • Oxidizing agents are added to act as a biocide, or to neutralize reducing agents.
  • Reducing agents are added to neutralize oxidizing agents, such as ozone and chlorine. They also help prevent the degradation of purification membranes.

I- Clarification:

• Clarification is a multi-step process to remove suspended solids. First, coagulants are added. Coagulants reduce the charges of ions, so that they will accumulate into larger particles called flocs.
• The flocs then settle by gravity in settling tanks or are removed as the water flows through a gravity filter. Particles larger than 25 microns are effectively removed by clarification.
• Water that is treated through clarification may still contain some suspended solids and therefore needs further treatment

II- Deionization and softening:

• Deionization is commonly processed through ion exchange. Ion exchange systems consist of a tank with small beds of synthetic resin, which is treated to selectively absorb certain cations or anions and replace them by counter-ions.
• The process of ion exchange lasts, until all available spaces are filled up with ions. The ion-exchanging device than has to be regenerated by suitable chemicals.
• One of the most commonly used ion exchangers is a water softener. This device removes calcium and magnesium ions from hard water, by replacing them with other positively charged ions, such as sodium.

III- Disinfection:

• Disinfection is one of the most important steps in the purification of water from cities and communities. It serves the purpose of killing the present undesired microorganisms in the water; therefore disinfectants are often referred to as biocides.
• There are a variety of techniques available to disinfect fluids and surfaces, such as: ozone disinfection, chlorine disinfection and UV disinfection.

Chlorine’s disadvantage:

• It can react to chloramines and chlorinated hydrocarbons, which are dangerous carcinogens.
• To prevent this problem chlorine dioxide can be applied. Chlorine dioxide is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. CI02 penetrates the bacteria cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organism.
• The by-product of this reaction is chlorite. Toxicological studies have shown that the chlorine dioxide disinfection by-product, chlorite, poses no significant adverse risk to human health.
• Ozone has been used for disinfection of drinking water in the municipal water industry in Europe for over a hundred years and is used by a large number of water companies, where ozone generator capacities up to the range of a hundred kilograms per hour are common.
• When ozone faces odors, bacteria or viruses, the extra atom of oxygen destroys them completely by oxidation. During this process the extra atom of oxygen is destroyed and there are no odors, bacteria or extra atoms left. Ozone is not only an effective disinfectant, it is also particularly safe to use.
• UV -radiation is also used for disinfection nowadays. When exposed to sunlight, germs are killed and bacteria and fungi are prevented from spreading. This natural disinfection process can be utilized most effectively by applying UV radiation in a controlled way.

3- Distillation:

• Distillation is the collection of water vapor, after boiling the wastewater. With a properly designed system removal of organic and inorganic contaminants and biological impurities can be obtained, because most contaminants do not vaporize.
• Water will than pass to the condensate and the contaminants will remain in the evaporation unit.

4- Electro dialysis:

Electro dialysis is a technique that employs electrical current and special membranes, which are semi permeable to ions, based on their charge. Membranes that permeate cations and membranes that permeate anions are placed alternately, with flow channels between them, and electrodes are placed on each side of the membranes. The electrodes draw their counter ions through the membranes, so that these are removed from the water.

5- pH-adjustment:

Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. The pH is brought up or down through addition of hydrogen chloride, in case of a basic liquid, or natrium hydroxide, in case of an acidic liquid. The pH will be converted to approximately 7 to 7.5, after addition of certain concentrations of these substances.