1. To list the largest global sources of water.
  2. To list the largest uses of water in the U.S.
  3. To list the major uses of water in the average U.S. home.


The earth contains about 326,000 cubic miles of water. Most of it is in the oceans (about 97%). However, water goes through phase changes (solid, liquid, gas), and its movement is ultimately driven by the sun. For example, the oceans ultimately supply the following 3 sources:


The U.S. supplies billions of gallons/day in water, but most of it is lost to:

Average U.S. water use has been steadily increasing, although not all of it has been for drinking. Typical uses include:

Average home uses include:

 Various fittings can save about 6-12 % in the average home (from toilets, showers, and laundry).


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The Safe Drinking Water Act (SDWA)    


The U.S. Public Health Service originally issued standards for drinking water. They developed the primary and secondary standards that were covered in our last lecture.    


1974 saw the passage of the Safe Drinking Water Act (SDWA). Several things were fundamentally different about this law:

The primary federal agency that oversees water quality is the Environmental Protection Agency. However, a number of federal agencies are involved with various aspects of water quantity and quality, including:

Progress in adding standards was slow, however, as scientists in 1974 were just beginning to detect many of the synthetic organics that find there way into water.  


Congress gradually became disenchanted with the EPA's progress, which led to the 1986 SDWA Amendments. This law required addition of 83 contaminants by 1989, and required adding 25 contaminants to the list every 3 years thereafter. Examples of new standards from this law include various VOCs in water, and inorganics such as aluminum, nickel, and beryllium. At the same time, the new law designated "best available technologies" for water treatment.    


The 1996 SDWA amendments canceled the schedule of 25 new standards every three years, and in its place set up a mechanism to set standards based on the occurrence and assessed risks of contaminants.   The law also authorized $1 billion in federal grants to individual states for upgrading water treatment systems. Research programs were set up for a consortium of American and Mexican Universities (especially for states on the Mexican border), for estrogen screening programs, and for general research.  

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Hard Water    

Objective: The purpose of this assignment is:

Hard water is water that contains hardness minerals (e.g., calcium, manganese and magnesium) above 1 GPG (grain per gallon). 1 GPG is equal to 17.1 PPM of water hardness as defined by Standard Methods. Hard water is not as efficient or convenient as "soft water" for bathing, washing (dishes, clothes or cars), shaving, and many other uses. For example:

If the hardness is over 3 GPG, softening can usually save enough to pay for the cost and maintenance of a water softener. Water softeners can also remove copper, iron, and other minerals. De-ionization is a more extensive form of water softening that removes anions as well as cations.


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Alternatives to Chlorination    


Objective: The purpose of this section is to analyze the alternatives to chlorination for their advantages and disadvantages (relative to traditional chlorination). A "+" means the alternative has a relative advantage over chlorination, and a "-" has a relative disadvantage relative to chlorination.

A. General considerations:
   +:  All the alternatives will reduce microbes and THM's
   -:  All the alternatives tend to cost more than chlorination
B. The alternatives:
   1. Chloramines:                                             
      +:  chloramine residual is more stable                          
      -:  chloramines need longer contact times                      
          chloramines may add taste and odor                               
          dialysis patients are susceptible                    
   2. Chlorine dioxide (ClO2):                                         
      +:  ClO2 more effective in disinfection                       
          ClO2 destroys many taste and odor compounds               
      -:  ClO2 must be generated on site                            
          no reliable test for the residual                    
   3. Iodine:                                                  
      +:  Iodine more effective in disinfection                       
          Iodine has little reaction with organics                        
          Iodine safe to transport                                    
          Iodine leaves a traceable residual                          
      -:  expensive                                            
          taste and odor                                       
   4. Ozone (O3):                                                   
      +:  Ozone more effective in disinfection                       
          Ozone destroys many taste and odor compounds               
      -:  Ozone must be generated on site                            
          Ozone has no residual protection                               
   5. U.V.:                                                    
      +:  no added taste or odor  
      -:  interference by turbidity                             
          viruses are especially resistant                      
          no residual protection                                
   6. Heat:                                                    
      +:  good for emergencies, no taste or odor added         
      -:  impractical for large scale                          
          no residual protection                              

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California Swimming Pools Standards

Objective: The purpose of this assignment is understand some of the minimum legal requirements for public pools in California for:


1. Free chlorine residual: at least 1 ppm is required. This is to be achieved by automatic hypochlorinators (units which provide for continuous chlorination) that are listed by NSF (the National Sanitation Foundation).

2. pH: must be between 7.2 to 8.0. If necessary, soda ash can be added to raise the pH. More typically, the pH naturally rises from the use of hypochlorites.

3. Other disinfectants: others may be used, provided that they are registered with the EPA for disinfectant use, and that they provide a protective residual.



4. Turbidity: the drain must be visible (this is, of course, the deepest point)

5. Filters: filtration units are similar in concept to units discussed for water treatment (e.g., diatomaceous earth filters)

6. Turnover time: this is the time it takes for a unit to filter the complete volume of a pool. The minimum legal standard in California is once every 6 hours for pools, and once every 1/2 hour for spas.



7. Lifesaving equipment: life rings must be at least 17 inches in diameter, with a line (rope) that is long enough to span the maximum width of the pool. Rescue poles (long poles with body hooks) must be at least 12 feet long.

8. Posted signs: if there is no lifeguard, a sign must be posted stating "Warning -- No Lifeguard On Duty."

9. Access: access to the pool must be limited by fencing (at least 4 ft. high) with gates that must be self closing and self latching.



10. Records: there must be daily records of maintainence (including chlorine levels, pH, etc.).

11. Spas, hottubs: high temperatures can be especially risky to the elderly; the powerful suction at the bottom of spas can also, in some cases be, risky. Numerous agents can be a risk in spas, including Pseudomonas aeruginosa (causing rashes). Naegleria fowleri, found in warm unfiltered waters, causes a deadly illness called PAM (primary amoebic meningoencephalitis).


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Terms related to the Hydrologic Cycle

"Water moves." This is probably the simplest way to summarize the hydrologic cycle. A typical diagram of the hydrologic cycle (water cycle) can be seen here. It's a reasonable place to start our discussion of water quality, and allows us to consider terms that relate to the solid, liquid, and gas phases of water.

Gas phase:

1. evaporation = to change to a vapor state

The oceans lose about 3 feet / year through evaporation.

2. transpiration = to give off water vapor through animal or plant pores.

Water can enter the vapor state not only through physical evaporation, but plants and animals play a significant role in introducing water into the atmosphere.

3. evapotranspiration = the combined effect of evaporation and transpiration.

Quite often, the distinction between evaporation and transpiration may be blurred; therefore, we often combine the terms.

Liquid phase

4. precipitation = rain, hail, sleet, snow, dew.

Water that enters the gaseous state can, of course, be returned to its source by precipitation. About 2/3 of this rain returns to atmosphere. Of the remainder, roughly 1/3 finds its way to groundwater; and 2/3 to surface water (in the U.S.).

Solid phase

5. watershed runoff = water flowing across land to receiving water

After precipitation, water travels across land. We can refer to this as urban runoff or rural runoff, each with its own set of issues (pesticides, animal waste, cars, oil, etc.).

6. percolation = to filter through (removes solids)

As water infiltrates downward through soil and rock towards groundwater, the filtering effect of this media can contribute to the clarity of typical groundwater sources.

7. leaching = liquids that remove soluble solids.

Unfortunately, the flip side of percolation is leaching, whereby harmful agents may accumulate in water traveling towards the grounwater.

8. dissolving = to pass into solution

Some materials dissole more easily than others, but remember that water is practically an ideal solvent.

9. capillarity = surface attraction between liquid and solid

Capillarity can be seen in a glass of water, if you look closely at the sides of the glass. The water does not end at a perfect 90 degree angle at the sides of the glass, but instead curves ever-so-slightly towards the sides. This is capillarity, and without it, our soils would not be able to hold moisture for very long. Capillarity becomes important in examing water in soils and groundwater.


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Terms relating to Groundwater

1. zone of aeration = vadose zone

This is the porous area between ground level and the beginning of a groundwater aquifer. This area is characterized by no free standing water (however, it does include capillary water).

2. zone of saturation: also called "aquifer" (latin for "water carrier")

This is a layer of underground sand, gravel, or porous rock that is saturated with water. It is the very source of groundwater.

3. confined aquifer = aquifers that are well below solid rock formations, and therefore more protected.

Sometimes referred to as "deep wells", confined aquifers can sometimes be some of the purest, highest quality of water available. Unfortunately, throughout the world, we are using up these aquifers.

4. porosity = the amount of water held by soil.

This amount is expressed as a % of the total volume. For example, if there are 100 cubic meters of an aquifer that has porosity of 50%, then we would have 50 cubic meters of water in this aquifer.

5. effective porosity = specific yield = % of total volume of water that drains freely from aquifer.

This term is quite different from porosity, because it is a fraction of the water. Continuing with our example with porosity, the 50 cubic meters of water may have an effective porosity of 60%, which means that 30 cubic meters (60% of 50 cubic meters) of water would drain freely from the aquifer. The significance of this measure is that it is not enough to know only the porosity -- we need to know how much of it we can actually access as a drinking source.

6. specific retention = % of total volume of water retained in aquifer

Specific retention is the complement to effective porosity -- in other words, the two values always add up to 100% (i.e., the water either drains freely or is retained). Continuing with our example, the specific retention would be 20 cubic meter of water (30 cubic meters that drains freely and 20 cubic meters that is retained is equal to 50 cubic meters of water),

7. water table = phreatic surface = the top of the zone of saturation.

As we use up our groundwater, the water table will be deeper belwo the ground. Phreatic surface is normally used in reference to the shape of the surface of the water table, often in reference to groundwater clean-up/



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Limnology is the study of lakes. In this module, we have two major concerns with limnology. Our first concern is the process of eutrophication. Eutrophication refers to the aging of a lake. The literal definition is "new nourishment", which refers to nutrients being continually added to a lake throughout its lifetime (e.g., increased levels of nitrates, phosphates). Eutrophication is normally a natural process that normally occurs over geologic time. However, pollution from humans can dramatically speed up this process. As a result, we refer to at least three types of lakes within this process:

1. oligotrophic = a young lake (early in the eutrophication process).

2. mesotrophic = medium-aged lake

3. eutrophic = an older lake (high in nutrients).

Our second concern that relates to eutrophication is the development of layers within a river. We can find the most layers in the summertime within a deep lake, as shown in the accompanying diagram. To these three layers we add the thermocline, defined below. These layers will become critical in our upcoming discussion of seasonal effects on water quality.

4. epilimnion = top layer of a lake or reservoir

5. metalimnion = middle or transition layer of a lake or reservoir

6. thermocline = area of the metalimnion with the largest temperature change

7. hypolimnion = bottom zone of stagnation in a lake or reservoir.



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Federal Drinking Water Standards

The list of federal drinking water standards is a large and growing one. However, this module presents an initial list that includes standards that have existed for some time. In the early history of the standards, a distinction was made between primary and seconary standards:

Primary standards refer to health based standards that are federally enforceable, usually in the form of an MCL (maximum contaminant level). The enforcement level in these standards is reflected in the legal language of "shall not exceed MCL."

Secondary standards refers to more aesthetically related guidelines given to the states (i.e., are not federally enforceable). The enforcement level in these standards is reflected in the legal language of "should not exceed MCL."

 We finish this module with a list of primary standards. With the clear warning that this list is not complete and the effects are not discussed in detail, this nevertheless starts an initial review of the range of health effects from contaminants in drinking water.



arsenic (As): GI tract

cadmium (Cd): kidneys

chromium (Cr): liver, kidneys



selenium (Se): neurotoxin

lead (Pb): anemia, kidneys, CNS

mercury (Hg): inorganic form: kidneys.

organic form: nervous system (Minamata disease)


barium (Ba): muscle stimulant

flourides (Fl): dental mottling

nitrates (NO3-): methemoglobinemia

silver (Ag) argyrosis (discolors skin,mucous membranes, whites of eyes)




1,1 dichloroethylene: liver and kidneys

p-dichlorobenzene: liver and kidneys

1,1,1 trichloroethane: liver, circulatory, nervous system






2,4,5-T cancer; 2,4-D; vinyl chloride; benzene; trichloroethylene; carbon tetrachloride; 1,2 dichloroethane; trihalomethanes


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Wastewater Characteristics 
I.  Physical characteristics                           

A. total solids content: solid residual matter that remains after evaporation.

We determine this value by simply boiling off the water -- whatever remains is the "total solids content." Perhaps the biggest surprise to most people about wastewater is that it is, in fact, mostly water! By analyzing the total solids content of wastewater, we know that it is typically 99% water and 1% solids. We can learn more, however, by dividing this value into two sub-categories described below: suspended solids and filterable solids.

1. suspended solids: this includes solids that are basically larger than1 micron in diameter.

When we flush the toilet, the fecal wastes have to go somewhere! Such wastes are, of course, part of the suspended solids. These wastes break up fairly quickly due to the action of water during transport. While fecal wastes are certainly part of this group, there may be many other sources (e.g., industrial wastes) depending on the sources of wastewater.

settleable solids: removed by gravity (usually in about one hour).

This is a sub-category of suspended solids. It is useful for us to know how much of the suspended solids will settle out in an hour, because these wastes are the easiest to remove.

2. filterable solids: This includes solids that are basically less than 1 micron in diameter.

These solids are much more difficult to remove from wastewater, because smaller particulates can remain suspended in water for a much longer time. In fact, they can pass through wastewater treatment facilities relatively unchanged. They generally fall into two sub-categories: colloidal and dissolved solids.

colloidal solids: This generally includes solids between 1 - 100 millimicrons in diameter.

dissolved solids: This generally includes wastes less than 1 millimicron in diamter.


II. Chemical characteristics                                                                                      

Without a doubt, we have historically devoted most of our attention to the removal of organics from wastewater. This is reflected by the different measures of organic pollution as described below. The first three measures are all labelled "oxygen demand." This refers to the amount of oxygen it takes to break down these organic wastes. In other words, instead of measuring all of the individual organic compounds, we have a general indicator (oxygen) for the strength of these wastes. As you'll see below, the oxygen plays a different role in each measure.

A. BOD (Biochemical Oxygen Demand)       
a measure of dissolved oxygen used by micro-organisms           
in the biological oxidation of organic matter.                 

BOD is perhaps the most relevant measure of organics, because most treatment methods for organic wastes involve the use of microbes to digest the wastes.

B. COD (Chemical Oxygen Demand)          
a measure of dissolved oxygen used by an chemical oxidizing agent  (potassium dichromate)        
in the chemical oxidation of organic matter.

COD is faster than BOD, because a powerful chemical oxidizing agent can oxidize organics faster than microbes. This makes it a more convenient measure, but less relevant to many treament methods.

COD is generally higher than BOD, because there are some organics that cannot be digested by microbes, but can be oxidized by powerful chemical agents.

C. TOD (Total Oxygen Demand)             
a measure of oxygen used 
in the incineration (physical oxidation) of organic matter. 

This is typically achieved by injecting wastes into a platinum catalyzed combustion chamber, where we measure the amount of oxygen present before and after incineration. The incineration techniques are the fastest of all. It's a useful measurement technique, but in terms of practical treatment methods, we would never actually be able to incinerate millions of gallons of wastewater every day.

D. TOC (Total Organic Carbon) 
a measure of the carbon that remains 
after the incineration (physical oxidation) of organic matter.            

Instead of using oxygen as the unit of measure, carbon becomes the unit of measure for this method, mostly from carbon dioxide that remains after complete combustion. We can measure this by infrared techniques. TOC is often used in the various models that predict the fate of different wastes, because it represents a more direct measure of the organics (i.e., all organics are composed of carbon).


A parting thought: we refer to each of the above measures as an "indicator." That is, they are general indicators of the level of organic pollution, and they help us calculate the amount of treatment that will be needed. There is a tremendous advantage in expressing the complex mix of organics in a single practical measure.

However, by the time we talk about inorganic wastes, there is no such common indicator! We generally have to measure these contaminants one chemical at a time. And that's expensive!



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Page updated: 2/07/02