Lesson 2_ Water Sources

7/11/2014 Lesson 2: Water Sources

http://water.me.vccs.edu/courses/ENV110/Lesson2_print.htm 1/7

Lesson 2: Water Supplies

Objective

In this lesson we will learn the following:

What types of water supplies are available for consumption.Different types of surface water supplies

Groundwater supplies

Reading Assignment

Along with the online lesson, read Chapter 2: Water Sources and Treatment, in your textbookOperation of Water Treatment Plants Volume I. (You may have already read this for lesson 1.)

Lecture

Introduction

The total amount of water in the world is almost constant. It is estimated to be 370,000 quadrillion

gallons, 97% of which is the water in the oceans, which is salty and unfit for human consumption

without an expensive treatment. The remaining 3% is known as fresh water, but 2% of that is theglacier ice trapped at the North and South Poles. Only 1% is available for drinking water.

Pure water is a colorless, odorless, and tasteless liquid. The depth and light give it a blue or bluish-

green tint. Tastes and odors in water are due to dissolved gases, such as sulfur dioxide and

chlorine, and minerals. Water exists in nature simultaneously as a solid (ice), liquid (water) and agas (vapor). Its density is 1 g/mL or cubic centimeter. It freezes at 0°C and boils at 100°C. When

frozen, water expands by one ninth of its original volume.

Water Supplies

There are two main water supplies: surface and ground.



Surface Water Supply

Surface water supply is the water from the lakes, reservoirs, rivers and streams. These water

bodies are formed of water from direct rain, runoffs, and springs. A runoff is the part of rain water

that does not infiltrate the ground or evaporate. It flows by gravity into thew water body from the

surrounding land. This drainage area is known as the watershed, which we will learn more about in

the next lesson. One inch of runoff rain/acre is equal to 27,000 gallons. Watershed characterists

affect the water quality, therefore protection of these watersheds is very important.

Surface waters can be classified into lentic (calm waters) and lotic (the running waters).

Lentic Water Supplies

Lentic waters are the natural lakes and impoundments or reservoirs. Natural lakes of good quality

water are very good sources of water. Impoundments are useful, as they eliminate seasonal flow

fluctuations and store water for adequate water supply, even under high consumer demand periods,such as drought in summer. Impounding also helps in the pretreatment of water by reducing

turbidity by sedimentation and reducing coliform bacteria and waterborne pathogens throughexposure to sunlight. Algal growth and other planktons, drifters formed of free-floating algae,

protozoans and rotifers, can cause taste and odor problems.

Normally, a natural lake goes through an aging process called eutrophication. It starts with abeautiful young lake and ends as a fertile piece of land. This process in nature is very slow; it takesthousands of years for a lake to disappear. Humans have accelerated this process by adding

nutrients and by discharging sewage, fertilizers, and detergents into lakes. There are three stages ofa lake: oligotrohpic, mesotrophic, and eutrophic.

Oligotrophic lakes are young, deep, and clear, with few nutrients. They have a few

types of organisms with low populations. An exaple of this type of lake is LakeSuperior.

Mesotrophic lakes are middle aged due to nutrients and sediments being

continuously added. There is a great variety of organism species, with low populatinsat first. As time increases the populatins increase. At an advanced mesotrophic stage a

lake may have undesirable odors and colors in certain parts. Turbidity and bacterialdensities increase. An example of this type of lake is Lake Ontario.

Eutrophic lakes, due to further addition of nutrients, have large algal blooms and

become shallower, with fish types changing from sensitive to more pollution-tolerantones. Over a period of time, a lake becomes a swamp and finally a piece of land.Lake Erie is progressing toward this stage.



Factors affecting lentic water quality include several factors, such as temperature, sunlight, turbidity,

dissolved gases and nutrients.

Temperature and stratification. Water has a maximum density (1 g/cm3) at 4°C. Above andbelow this temperature water is lighter. Temperature changes in water cause stratification, or

layering, of water in lakes and reservoirs. During the summer, the top water becomes warmer thanthe bottom and forms two layers, with the top one warmer and lighter and the bottom one cooler

and heavier. During the fall as the temperature drops and the top water reaches 4°C, it sinks to thebottom and the bottom water moves to the top. This is known as fall turnover. This condition stirs

the bottom mud and releases the anaerobic decomposition products such as sulfur dioxide andother odor-causing chemicals that cause severe tase and odor problems. In the winter too muchsnow cover for longer time periods can cause oxygen depletion by reducing light penetration, thus

the lower rate of photosynthesis. This condition is can cause winter fish kill. In spring, as the icemelts, and the temperature at the surface reaches 4°C water sinks once again to the bottom and

results in the spring turnover, which, like fall turnover, can cause taste and odor problems.

Light. Light, the source of energy for photosynthesis, is important. The rate of photosynthesisdepends on the light intensity and light hours per day. The amount of biomass and oxygen

production corresponds to the rate of photosynthesis. The amount of dissolved oxygen (DO) in thelakes is maximum at 2 p.m. and minimum at 2 a.m.

Turbidity. Turbidity affects the rate of the penetration of sunlight, and thus, photosynthesis. The

more turbidity, the less sunlight can penetrate, which lowers the rate of photosynthesis andconsequently less DO.

Dissolved gases. These are mainly carbon dioxide (CO2) and oxygen (O2). Carbon dioxide is

produced during respiration and is used in photosynthesis; oxygen is produced during

photosynthesis and is needed for respiration. DO is consumed by the microorganisms for theaerobic decomposition of biodegradable organic matter. This oxygen demand of the water is

known as biochemical oxygen demand (BOD). The more the BOD, the less DO in the water. Themore the DO, the better the quality of water. The minimum amount of DO to maintain normal

aquatic life, such as fish, is 5 mg/L.

Lotic Water Supplies

Rivers, streams and springs are lotic water supplies.

Factors affecting lotic water supplies are much smaller than those affecting lakes and reservoirs.

The only factors affecting running water is current and nutrients.

Current. It is the velocity or rate of flow of water. The faster the current, the better it is. Current

mixes the oxygen from the atmosphere and keeps the bottom of the stream clean by wasing away

the settlable solids. There is more DO and less natural organic matter that would otherwise



decompose in the bottom. Thus, due to the current, streams and rivers seldom go anaerobic.

Nutrients. Main sources of nutrients are drainage from the watershed. Heavy rains and droughtconditions can also cause serious problems, such as high turbidity and more nutrients.

Surface water supply is the most contaminated supply, mainly due to discharge of sewage, used

water, which is the source of waterborne pathogens, runoffs from farmland, which are the source of

Cryptosporidium, pesticides, and fertlizers; and industrial discharges, which are the source of a

variety of contaminants. Surface water, therefore, needs the maximum treatment for potability(satisfactory for drinking).

Groundwater Supplies

Underground water is supposed to be the purest form of natural water. Sometimes, it is so pure

that it does not need any further treatment for drinking purposes. It is the least contaminated andhas very low turbidity due to natural filtration of the rain water. It can be contaminated by

underground streams in areas with limestone deposits, septic tanks discharge, and underground

deep well leaks. Therefore, it may need disinfection. It needs only mineral removal treatment whencompared to surface water supplies. It contains more dissolved minerals such as calcium,

magnesium, iron, manganese and sulfur compounds than the surface supply. There are two sources

of groundwater: springs and wells.

If you dig a hole down through the earth, the soil initially has pockets of air between the soil

particles. But as you dig deeper, soon water would fill in all of the gaps in the soil. The location

where all of the holes first become filled with water is called the water table. This is the upper limit

of the zone of saturation, also known as an aquifer, which is the part of the earth containing thegroundwater.

The bottom of the zone of saturation is marked by an impermeable layer of rocks, clay or other

material. Water cannot soak through this layer, so it instead slowly flows downhill.



Springs

Whenever an aquifer or an underground channel reaches the ground surface such as a valley or a

side of a cliff, water starts flowing naturally. This natural flow is known as a spring. A spring may

form a lake, a creek, or even a river. The quantity and velocity of a spring flow depend on the

aquifer size and the position of the spring relative to the highest level of the water table. Regionswith limestone deposits have large springs as the water flows in underground channels, formed by

the erosion of limestone. The quality of the water depends on the nature of the soil through which

the water flows. For example, a mineral spring has dissolved minerals, a sulfur spring has dissolved

sulfur.

Wells

Public groundwater supply is usually well water because springs are rare. A well is a device to

draw the water from the aquifer. Deeper wells (more than 100 feet) have less turbidity, more

dissolved minerals, and less bacterial count than shallow wells. Shallow wells have less naturalfiltration of water due to less depth of the soil.



Small rural communities (less than 25,000 populations) generally use the groundwater from wells.

About 35% of the American population uses groundwater supply.

Review

There are two main water suppllies used for consumption: surface water and groundwater. Surface

waters include calm waters, such as lakes and reservoirs, and running water, such as a river or

stream. Factors affecting calm water quality include several factors, such as temperature, sunlight,turbidity, dissolved gases and nutrients. Factors affecting running water supplies are much smaller

than those affecting lakes and reservoirs. The only factors affecting running water is current and

nutrients.

Underground water is supposed to be the purest form of natural water. Sometimes, it is so pure

that it does not need any further treatment for drinking purposes. It is the least contaminated andhas very low turbidity due to natural filtration of the rain water. The two main supplies of

groundwater are springs and wells. Whenever an aquifer or an underground channel reaches the

ground surface such as a valley or a side of a cliff, water starts flowing naturally. This natural flow is

known as a spring. A well is a device to draw the water from the aquifer. Deeper wells (more than

100 feet) have less turbidity, more dissolved minerals, and less bacterial count than shallow wells.

Assignment

Work the following crossword puzzle that comes from definitions in your textbook. You may either

print the puzzle out, complete it and mail or fax back to the instructor or you may send an email

with the correct answers numbered accordingly.

http://water.me.vccs.edu/courses/ENV110/crosswords/lesson2.pdf



Quiz

Answer the questions in the Lesson 2 quiz . When you have gotten all the answers correct, print

the page and either mail or fax it to the instructor. You may also take the quiz online and submit

your grade directly into the database for grading purposes.

http://water.me.vccs.edu/courses/ENV110/quiz2.htm

Documents

Lesson 2_ Water Sources