Water Quality

Introduction

The topic of water quality focuses on the presence of foreign substances in water and their effect on people or the aquatic environment. Water of good quality for one purpose may be considered to be of poor quality for some other uses. For example water suitable for swimming may not be of good enough for drinking. But even drinking water may not be suitable for certain industrial purposes that require pure water. However it is necessary to determine what substance are ¡n the water and in what concentrations they are present. Finally, some standards against which to compare the result of the water quality analysis and thereby judge the suitability of the water for a particular use are needed.

Water has a remarkable tendency to dissolve other substances. Because of this it is rarely found in the nature in a pure condition. Even water in a mountain stream, far from civilization, contains some natural impurities in solution and suspension. The changes in water quality begin with precipitation. As rain falls through the atmosphere it picks up dust particles and such gases as oxygen and carbon-dioxide. Surface runoff picks up silt particles, bacteria. Organic materials and dissolved minerals. Ground water usually contains more dissolved minerals than surface water because of its longer contact with soil and rock, Finally water quality is very much affected by human activities including land use (agriculture) and the direct discharges of industrial or municipal waste water to the environment.

Impurities in the Natural Water

Suspended particles

Colloidal particles

Dissolved particles & gases

Suspended Particles (settleable) -

Size is I pm — 200 pm. These are large enough to be removed by filtration or sedimentation. Suspended impurities are bacteria, algae (These are small weeds like plants growing in water which is exposed to sunlight), fungi (These are small plants growing in water in the absence of sunlight), clay, silt, & sand.

Colloidal Particles (fine particles)

Size Is 0.001 pm - 1 pm. Clay, Silica are examples. These are not possible to be removed by ordinary
sedimentation. These impurities remain in continuous movements as these are electrically charged due to presence of absorbed iron on the surface of the soil particles.

Dissolved Particles & Gases.

Size is less than 0.001 pm. These impurities mainly contain organic compounds, salts (Calcium/Magnesium/Sodium Carbonates/Sulfates/Chlorides etc.) and gases (Oxygen, Carbon Dioxide, Hydrogen Sulfide, Nitrogen etc.).

Sub-Surface Sources (Underground Sources)

General

The water which gets stored in the ground water reservoir through infiltration, percolation etc. is known as underground water. This water is generally pure, because it undergoes natural filtration during the percolation through soil pores. More over these waters are less likely to be contaminated by bacteria. However they are generally rich in dissolved salt, minerals, gases etc. Sometimes the ground water is brought to the surface by some natural source like springs, and sometimes these waters a; tapped by artificial means by constructing wells, infiltration galleries etc.

Occurrence of Ground water

All the materials of variable porosity near the upper portion of the earth’s crust are places of the potential storage for ground water. This storage of ground water is sometimes referred to as the Ground water Reservoir. . The possibility of occurrence of ground water mainly depends upon two properties of the underground soil, they are;

• Porosity
• Permeability

Porosity is the quantitative measurement of the voids present in the soil; which is the ratio of the volume of voids and the total volume given as a percentage. Porosity values of some common rock formation are as given below,

Permeability is defined as the ability of a rock or unconsolidated sediment to transmit or pass water through itself and is generally measured in terms of Coefficient of Permeability.

Type of rock formation	Porosity	Coaff. Of Permeability (cm/sec)
Granite, Quartzite	1.5%	0.000006
Lime stone	5 to 10%	0.00004
Sandstone	10 to 15%	0.004
Sand and Gravel	20 to 30%	0.4
Only Gravel	25%	4.0
Only Sand	35%	0.04
Clay and Soil	45%	0.0000004

Aquifers and Their Types

A permeable stratum or geological formation of permeable material, which is capable of yielding appreciable quantities of ground-water under gravity, Is known as an aquifer.

An aqulclude is an impermeable body of rock or stratum of sediment that acts as a barrier to the flow of groundwater.

(Aquifer and Aquicludes)

Aquifers vary in depth, lateral extent, and thickness; but in generally fall into one of the following two categories. The top most water bearing stratum having no confined Impermeable overburden (i.e. an aquiclude) laying over it, is known as Unconfined Aquifer or Non-artesian Aquifer.

When an aquifer Is confined in Its upper-and under surfaces, by impervious rock formations (i.e. aquiciudes), and is also broadly inclined so as to expose the aquifer somewhere to the catchment area at a higher level for the creation of sufficient hydraulic head, it is called Confined Aquifer or an Artesian Aquifer.

Non – artesian or Unconfined aquifer and well

Confined or Artesian aquifer and wells

Different Forms of Underground Sources

The underground water is generally available in the following forms.

Wells and Tube wells

Springs

Infiltration Wells

Infiltration Galleries

Wells and Tube Wells

Water well is a hole usually vertical, excavated in the earth for bringing ground water to the surface. The wells may be classified in two cases: i.e. Open Wells or Dug Wells and Tube Wells.

Open wells are generally open masonry wells having comparatively bigger diameters, and are suitable for low discharges say about 5 liters/sec or less. The diameters of open wells may vary from 1 to 9 meters, and are generally less than 20 meters In depth.

Tube Wells, which is sometimes called as deep wells, is a long pipe bored or drilled deep into the ground, intercepting one or more water bearing strata (aquifers). Generally deep wells are drilled to an aquifer below an impervious layer like clay. The water in deep tube wells gets purified due to natural filter, but is usually hard as it contained dissolved salts. They are generally 0.15 to 0.6 In diameter and may be deep as deep as 70 to 200 meters.

A Strainer tube well

Cavity type tube well

Cavity formation in Dig wells

Static Water Level Is the level at which water stands In a well in relation to the ground level. Draw Down is the extent to which the static water level Is reduced as a result of pumping. The draw down is also known as the depression of the water table. Cone of Depression is the solid cone formed between the water bearing stratum and the depressed water level In the well.

Springs

The natural outflow of ground water at the earth’s surface is said to form a spring. A pervious layer sandwiched between two impervious layers give rise to a natural spring. These are generally capable of supplying small amounts of water and are not considered as a good source of supply.

Gravity spring                                                                        Artesian spring

Infiltration Wells

Infiltration wells are the shallow wells constructed In series along the bank of a river, In order to collect the river water seeping through their bottoms.

Infiltration Galleries

Infiltration galleries are the horizontal tunnels. Constructed at shallow depths such as 3 to 5 meters along the banks of rivers, through water bearing strata. They are sometimes called horizontal wells. These galleries are generally constructed of masonry walls with roof slabs, and extract water from the aquifer by various porous drain pipes. .

Artesian spring

Factors Governing the Selection of a Particular Source of Water

• Quantity of available water
• Quality of available water
• Distance of the source of supply
• General topography of the intervening area
• Elevation of the source of supply

Location if infiltration wells                             Section of an Infiltration gallery

Sources of Water

Introduction
After estimating the water requirement for a proposed water supply scheme, the planners must search for the water resources which are able to supply the required amount of water. If the available sources near to the scheme (place where the water is needed) Is of sufficient or suitable, planners should search for sources at far distances and provide arrangement for bringing water from there.
Classification of Sources of Water
The various sources of water available on the earth can be classified in to following two categories.
Category 1 »»»  Surface Sources
Category 2 »»»  Sub-Surface Sources (Underground Sources)
Surface Sources
Surface Sources are those Sources of water in which the water flows over the surface of the earth or accumulated on the surface of the earth and is thus directly available for water supplies. Following are the different types of the surface sources.

• Ponds and Lakes
• Streams and Rivers
• Storage Reservoirs
• Oceans

Ponds and Lakes .
A natural large sized depression formed within the surface of the earth, when gets filled up with water, is known as a pond or a lake. The difference between a pond and a lake Is only that of size, If the size of the depression is comparatively small, It may be termed as a pond, and when the size Is larger it may be termed as a lake. Generally, the surface run-off from the catchment area contributing to the particular lake enters the lake through small drains or streams.
The quality of water in a lake is generally good and does not need much purification. Larger and older lakes however provide comparatively purer water than smaller and newer lakes. Self-purification of water due to sedimentation of suspended matter, bleaching of color, removal of bacteria, etc. makes the lake’s water purer and better. On the other hand, in still waters of lakes and pond, the algae, weed and vegetable growth take place freely, imparting bad smells, tastes and colors of their waters.
The quantity of water available from lakes Is, however, generally small. ¡t depends upon the catchment area of the Lake Basin, annual rainfall, and geological formations. Due to the smaller quantity of water available from them, takes are not considered as principal sources of water supplies. They are, therefore, useful for only small towns and hilly areas. However, when no other Sources are available, larger lakes may become the principal sources of supplies,
Streams and Rivers
Small Steam channels feed their waters to the lakes or rivers. Small steams are, therefore generally not suitable for water supply Schemes, because the quantity of water available in them is generally very small, and they may even sometimes go dry. They are, therefore useful as sources of Water only for small villages especially in hilly regions etc. across them.
Rivers are the most important sources of water for public water supply schemes it is a well-known fact that most of the cites are settled near the rivers, and it is generally easy to find a river for Supplying Water to the city. Rivers may be perennial or non-Perennial Perennial rivers are those in which the water IS available through0 the year. Such rivers are generally fed by rains dung rainy season and by Water springs, snow etc. as the case may be, during dry season, Perennial avers can be used as sources of public supplies directly, whereas the non-perennial rivers can be used as sources of public Supplies by Providing storage on the upstream of the intake Works, The concoction of a dam is generally adopted on a highly non Perennial river and may be adopted even on a perennial river when water is used for multiple uses such as irrigation hydropower etc. The head works, such as a barrage or a Weir, may also
be constructed on those perennial rivers, ere supplies are considerably reduced during dry weather periods. The quality of water obtained from rivers is generally not reliable as it contains large amount of sift, Sand and a lot of suspended matter, the disposal of the untreated or treated sewage into the dyers is further liable to contaminate their waters, The river waters must, therefore be properly analyzed and well treated before Supplying to the public.
A water Supply scheme drawing water directly from a river or a stream may fail to satisfy the Consumer’s demands during extremely low flow, while during high flows; ¡t may again become difficult to carry out its operations due to devastating floods. A barrier in the form of a dam may, therefore sometimes be constructed across the river, so as to from a pool of water on the upstream side of the barrier, this pool or artificial lake formed on the upstream side of the dam is known as the storage reservoir, The quality of this reservoir water is not much different from that of a natural lake. .
The water stored in the reservoir can be used easily not only for water supplies but also for other purposes. Generally, multipurpose reservoirs are planned these days and operated so as to get optimum benefits, The subject of design and planning of dams and reservoirs is a big topic in itself, and is not dealt under this subject. However, its salient features such as : Selection of dam site and types of dam; Storage capacity of reservoirs, Reservoir
sedimentation, Reservoir losses, etc. are however being reproduced here, ,
Selection of a Dam Site,

A suitable foundation must be available.
Length of the dam should be as small as possible.
Suitable site for the spillway should be available.
Materials for construction should be easily available.
Reservoir basin should be reasonably water tight.
Value of the land and property submerged by the reservoir should be as low as possible.
Site should be easily accessible.
Site and the reservoir should be environmentally feasible.

Different kinds of Dams

• Earth dams
• Rock-fill dams
• Solid masonry gravity dams ‚

Storage Capacity of Reservoirs.
Whatever be the size or the use of a reservoir, the main function o it is to store water, and thus to stabilize the flow of water. Therefore the most important physical, characteristic of the reservoir is its storage capacity. Storage capacity of a reservoir in a given dam site is calculated and analyzed using Area- Capacity diagrams, Fixing a storage capacity for a given data of available water and the particular requirement of water is done by different methods such as Mass Flow Curves,
Derivation of Reservoir Capacity — Mass Flow Curves
              A Mass flow curve is a curve of cumulative reservoir inflow against time and as such it rises continuously. Any point on the curve indicates the total inflow from the beginning of the period up to the given time. The slope of the tangent to the Mass Curve is a measure of Inflow at that time. A steeply rising curve indicates high rate of inflow. Mass Curve of Demand representing accumulated outflow is also plotted. For a uniform rate of demand the Demand Curve is a straight line, rising from the origin.
Reservoir Losses

• Evaporation losses
• Absorption losses
• Percolation losses or Reservoir Leakage

Intakes for Collecting Surface Water
Whenever the water Is withdrawn from a surface water source such as a lake, river or a reservoir, and the entrance of the withdrawal conduit (pipe) Is riot an integral part of the darn or any other related structure, then an intake structure must be conducted at the entrance to the withdrawal conduit (pipe). The water collected at the intake structure could then be taken by gravity flow (if possible) or by pumping up to the treatment plant. It is very important to construct the intake structure site at a proper location. The factors governing the location of an intake structure are as follows,

As far as possible the Intake should be near the treatment plant
The intake must be located in the purer zone of the source.
The Intake must never be located at the downstream or in the vicinity of a point of disposal of waste water
The intake should paver be located near navigation channels
The intake site should be such that it will permit grater withdrawals of water, if required in the future.
The intake must be- located at a place where it can draw water even during driest periods
The intake site should be easily accessible even during floods and should not get flooded.
In meandering rivers, the intake should not be located on curves as much as possible. Even if they have to be located on curves It should be located on the concave banks.

                        Simple Concrete block – Submerged intake

Medium Size River intake

River intake arrangement when an approach channel leads the river to sump well

Canal intake well

The Consumptive Pattern throughout the Day

The Consumptive Pattern throughout the Day

Annual average demand is not sufficient for the design of various component of a water supply scheme. There are wide variations in the use of water in different season, in different months of the year, ¡n different days of the months, in different hours of the day.

The consumptive patterns of water used will produce hourly variations in the demand. in the absence of actual field data, the following pattern of consumption may be assumed Until data becomes available:

The daily demand varies throughout the day with peak demands in early morning and late afternoon.

Maximum hourly consumption is generally taken as 150% of the days normal consumption rate.

Maximum hourly consumption = 1.5 x average hourly consumption

Provision for Growth in Population

When estimating the population figures for a water supply scheme, the provisions have to be made for the future growth the population, as calculated by the equation given below.

Design Population

Where,

P = present population

r = Population growth rate (r=1 .5% rural, and 2,5% urban)

n = number of years forecasting

Introduction to Water Supply

Water
Water Is a commonly available chemical substance on earth, which is essential for all known forms of life, In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth’s surface. On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water.b1ow ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air, and precipitation. Oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth’s water is contained within biological bodies and manufactured products.
Clean, fresh drinking water is essential to human and other life forms. Access to safe drinking water has improved steadily and substantially over the ‘last decades in almost every part of the world. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.
Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of freshwater is consumed by agriculture.

Movement of Water in Nature

Water on Earth moves continually though a cycle of evaporation or transpiration (evapo-transpiration), precipitation, and runoff, usually reaching the sea. Most of the earth’s water sources get their water supplies from precipitation, which may tall in various forms, such as rain, snow, hail, dew etc. Rains, no doubt form the major part of the supplies. Since the precipitation is the principal source of water on the earth, It is worthwhile to study the overall hydrologic phenomenon of movement of water, which described by the Hydrologic cycle. Unlike other commodities, water is not manufactured. Instead it is continuously re-cycled naturally through many different forms. This cycle, called the hydrological cycle, involves evaporation, transpiration, evopo-transpiration, condensation, precipitation, infiltration, percolation and runoff.
An understanding of hydrological cycle helps to explain the way in which all water becomes available.

Water Consumption for Different Purposes

Water has always played a prominent role in human civilization. When people first began settling in one place and growing crops for sustenance, it was invariably near water sources like rivers, lakes, or groundwater springs. Water is regarded as commonplace because it is the most plentiful liquid on earth. and for decades people used water as though there. Supply would never fall. Water may be common place but useful water is not always readily available in many parts of the world today.
Drinking water means water for human consumption and hygiene. Drinking water can come from both surface water and ground water.
People needs Water for

• Drinking
• Preparing food
• Bathing
• Cleaning and
• a variety of other tasks

The water sources used for supplying water were not always clean however and treating drinking water to improve smell taste, clarity, or to remove disease-causing pathogens has occurred in one form or another throughout recorded history. The safety and accessibility of drinking-water are major concerns throughout the world.
The health risks may arise from consumption of Water contaminated with infectious agents, toxic chemicals and radiological hazards. Improving access to safe drinking-water can result in tangible (visible) improvements to health.
The Per Capita Demand and the Factors Affecting the Per Capita Demand
It is the annual average amount of daily water requirement by one person and Includes the domestic industrial commercial, public & waste. it may be expressed as lpcd (liters per capita per day).
The per capita demand based on annual average daily consumption per person.

Per capita demand per day (Ipcd) = Total yearly water requirement of the city In liters /(365 x Design Population)

Factors affecting the per capita demand

• Size of city .
• Climatic condition
• Habits of people
• Industrial & commercial activities
• Quality of water
• Pressure in the distribution system
• Development of sewage facilities
• System of supply
• Cost of water
• Policy of water consumption
• measurement (Metering)
• Method of charging (tariff-slabs)

Variation in Demand from the Average
Types of Water Demands
Domestic Demand : Depend on three main factors

Type of Connection → House Connections, stand Posts (45 lpcd)
Type of Area → Urban, Rural
Climatic Condition → Wet, Dry
Non Domestic Demand

• Government Institutions
• Shipping & ports .
• School - Day Schools (15-30 ipcd) / Boarding Schools (90-140 lpcd)
• Hospitals (220-300 Ipcd)
• Public places — e.g. Parks, bus stands
• Other offices.
• Industries - Water based Industries / Non-water based Industries
• Commercial Institutions
• Tourist Hotels
• Restaurants
• Shops
• Service Stations
• Cinemas
• Religious Institutions

Un Accounted water

• Losses
• Fire Demand

Total Water requirement = Accountable Water + Un-Accountable Water
Accountable Water = Domestic Demand + Non- Domestic Demand
Un-Accountable Water = (12-20%) of accountable Water

Technorati Tags: Water,people,waste water,water supply,water demand,Lpcd,per capita demand

Water and Wastewater Engineering : Water Quality

Water and Wastewater Engineering

Water Quality Introduction

The topic of water quality focuses on the presence of foreign substances in water and their effect on people or the aquatic environment. Water of good quality for one purpose may be considered to be of poor quality for some other uses. For example water suitable for swimming may not be of good enough for drinking, But even drinking water may not be suitable for certain industrial purposes that require pure water. However it Is necessary to determine what substance are in the water and In what concentrations they are present. Finally, some standards against which to compare the result of the water quality analysis and thereby judge the suitability of the water for a particular use are needed. .

Water has a remarkable tendency to dissolve other substances. Because of this it Is rarely found in the nature in a pure condition. Even water In a mountain stream, far from civilization, contains some natural impurities in solution and suspension. The changes in water quality begin with precipitation. As rain falls through the atmosphere it picks up. dust particles and such gases as oxygen and carbon-dioxide. Surface runoff picks up silt particles, bacteria, organic materials and dissolved minerals. Ground water usually contains more dissolved minerals than surface water because of its longer contact with soil and rock. Finally water quality is very much affected by human activities including land use (agriculture) and the direct discharges of industrial or municipal waste water to the environment.

Impurities in the Natural Water

• Suspended particles
• Colloidal particles
• DIssolved particles & gases

Suspended Particles (settleable)

Size is 1 pm —200 pm. These are large enough to be removed by filtration or sedimentation. Suspended impurities are bacteria, algae (These are small weeds like plants growing in water which is exposed to sunlight), fungi (These are small plants growing in water in.the absence of sunlight), clay, silt, & sand.

ColloIdal Particles (fine particles)

Size is 0.001 µm - 1 µm. Clay. Silica are examples. These are not possible to be removed by ordinary
sedimentation. These impurities remain in continuous movements as these are electrically charged due to presence of absorbed iron on the surface of the soil particles.

Dissolved Particles & Gases .

Size is less than 0.001 pm. These Impurities mainly contain organic compounds, salts (Calcium/Magnesium/Sodium Carbonates/Sulfates/ Chlorides etc.) and gases (Oxygen, Carbon Dioxide, Hydrogen Sulfide, Nitrogen etc.).

Characteristics of Water

There are three broad type of characteristics needed In analysis of the quality of water required for water supply.

They are

• Physical characteristics
• Chemical characteristics
• BiologIcal characteristics