1) What does it cost (per gallon?) now for large municipal water
systems (>100,000 people) to make water potable?

2) How many gallons per day per person does a municipal water
treatment plant
need to output?

3) How do the large systems go about removing arsenic and other
impurities from water?

Cite all sources, please.

Hi dgc,

Ok, I got your facts and figures for you, at least as close as I could
find.  Please note that, unless specified otherwise, all figures below
are from US sources and are in US dollars.

=======================
COST TO PURIFY WATER
=======================

There were several difficulties in ascertaining this number. First,
most municipalities do not separate the cost of purifying water from
the cost of maintaining water plants and distributing water ---

“… the steps involved in providing drinking water. These include the
cost of maintaining 21,250 acres of watershed, capturing, treating and
storing water, and distributing it over 895 miles of pipeline. There
are also other substantial capital costs of the physical plant
facilities, like pumping stations, storage tanks and treatment plants.
http://www.marinwater.org/howratesdetermined.html

Also the source of the water has a big effect on the cost of purify
that water. See the benchmarks below for the ranges.


BENCHMARKS--------

Water treatment Expenses - averages for year 2000 -------

Class AB Utilities With Own Source of Ground Water
Per million gallons of water sold -- $90.94

Class AB Utilities With Own Source of Surface
Water – various lakes

Per million gallons of water sold  -- $624.04
Per million gallons of water sold -- $181.75

Class AB Utilities With Purchased Water
Per million gallons of water sold - $16.61

Class C Utilities With Own Source of Ground Water
Per million gallons of water sold  -  $127.45

Class C Utilities With Purchased Water
Per million gallons of water sold  -- $1,436.59

Public Service Commission of Wisconsin
http://psc.wi.gov/water/newsinfo/document/bnch2001.pdf


OTHER SOURCES FOR COSTS ---


Approximate cost to treat municipal drinking water is between $75 per
million gallons and $95 per million gallons.

This number is from a comprehensive study where researchers in
Nebraska, Texas, and Oregon collaborated to provide information on how
the volume of pollutants affects the marginal costs of treating
municipal water supplies.

The study is here –

COSTS OF WATER TREATMENT DUE TO DIMINISHED
WATER QUALITY: A CASE STUDY IN TEXAS
http://ageco.tamu.edu/faculty/mccarl/papers/535.pdf

And is summarized here ---

URBAN WATER CONSORTIUM
http://www2.ncsu.edu/ncsu/CIL/WRRI/uwc/oct98dimqual.html

TAMU – NEW WAVES - ABSTRACT
http://twri.tamu.edu/twripubs/NewWaves/v11n1/abstract-1.html

---------------------

One more reference which corroborates the above --

“… This process (including sediment disposal) adds a cost of $20.00
per million gallons of water treated (or $75.84 per day for the H.D.
Taylor treatment plant in Oregon). This figure does not include
filtration costs  … This gives an annual average municipal treatment
cost of $1,015,472 , or a savings of $201,186 if half the sediment
were removed.”

The Benefits of Watershed Management: Water Quality and Supply
http://www.pcl.org/Land%20Use/section4.html

---------------------------

In Ontario Canada, municipalities were required to file a Year 2000
report which included cost per million litres to treat water supplies.
To read those reports, search:

“municipal water treatment” Ontario “per million litres”
://www.google.com/search?sourceid=navclient&q=%22municipal+water+treatment%22+Ontario+%22per+million+litres%22

* remember that amounts are in Canadian dollars. 

======================
WATER USAGE
======================

Publicly supplied water can be divided into major water-use categories
as follows: domestic, commercial, industrial, public use and losses,
and thermoelectric power (representing less than 1 percent).

For domestic water (water used for normal household purposes), the
average consumption per person per day is estimated at 80 gallons.

Total water use for all categories is estimated at 402 billion gallons
per day of fresh and saline water. Divide this by number of people in
the US (281 million)  = 1,430 gallons per person.


--------------------------

USGS – 1995 WATER USE
http://water.usgs.gov/watuse/pdf1995/html/

------------------------

UNIVERSITY OF KENTUCKY – COOPERATIVE EXTENSION – WATER USAGE
http://www.ca.uky.edu/enri/pubs/usage.pdf


=================================
METHODS OF WATER PURIFICATION
==================================

There are many different steps to the drinking water purification
process which are used. What a municipality uses depends on the exact
components that make up the impurities in their water supply. In
general the processes are ---

Filtration
Precipitation
Disinfecting 
Distillation 
Reverse Osmosis 


KENT STATE UNIVERSITY – WATER PURIFICATION
http://www.stark.kent.edu/~cearley/ChemWrld/waterpure/water.htm

-----------------------------------------

Detailed explanation of every possible step and method can be found
here –

“MUNICIPAL OR UTILITY WATER TREATMENT
Most municipal water found in a city or community today has been
treated extensively. Specific water treatment methods and steps taken
by municipalities to meet local, state, national, or international
standards vary but are categorized [in the document below.]”

Methods of Water Purification 
By: Osmonics Inc.
Published in: National Development
http://www.osmonics.com/products/Page716.htm


=========================
OTHER RESOURCES
=======================

EPA – OFFICE OF WATER
http://www.epa.gov/water/index.html


EPA: Public Drinking Water Systems: Facts and Figures
http://www.epa.gov/safewater/pws/factoids.html

AMERICAN WATER WORKS ASSOCIATION – REPORT  (for purchase)
http://www.awwa.org/Communications/h20stats/wsdetail.cfm

AMERICAN WATER WORKS ASSOCIATION – PRICES
http://www.awwa.org/Communications/h20stats/PriceTab.cfm



So, that should answer your question. If anything I’ve said isn’t
clear, please feel free to ask for clarification. Thanks for your
question.

-K~

Search terms:

“gallons per person” water statistics
municipal water purification costs
municipal water purification methods
"municipal water treatment"  "per million litres"
"Municipal Water Treatment" COST
municipal water supply purification cost
"dollars per gallon" drinking water
"cost to treat water" municipal

Knowledge-Seeker did a very good job on this report. It was certainly
quick--always good for the first three stars in my book, so long as
the answer is there as well (sometimes it isn't!). The fourth star was
for comprehensiveness of the response. It relied, perhaps, too much on
regional rather than cumulative national resources and some of the
data was not entirely pertinent to the questions asked; however, the
regional resources were well chosen and the documentation/citations
were complete. A solid B+/A-.

1.  Cost figures will vary from supplier to supplier, so the
Massachusetts Water Resources Authority will be used as

an example.  The MWRA supplies potable water to 2.2 million people in
the greater Boston area.  It also provides

wastewater treatment services, as well. 

The MWRA's potable water demand in calendar year 2001 was 247 million
gallons per day:
http://www.mwra.com/water/html/wsupdate.htm

The MWRA's financial statement states that operating expenses for the
drinking water operation in fiscal year 2001

were US $70,437,000:
http://www.mwra.com/org/html/rates_FS02.PDF

This puts the operating expense at approximately US $0.0007813 per
gallon (0.07813 cents per gallon).  This is just

for operating expenses only, excluding debt service, capital
expenditures on system improvements, etc.

The pay-as-you-go wholesale rate it charges for potable water in
fiscal year 2002 is US $1,396 per million gallons, or

US $0.001396 per gallon (0.1396 cents per gallon).  Most of the cities
and towns the MWRA services are charge set

dollar amounts, based on their historical water usage.
http://www.mwra.com/org/html/rates_water.htm


2.  According to the American Water Works Association, a professional
organization of individuals in the water

treatment industry:

"Each person uses about 100 gallons of water a day at home."
http://www.awwa.org/advocacy/learn/INFO/425FACTSABOUTWATER.CFM


3.  The US EPA summarizes the most common water treatment techniques
as:

"Water suppliers use a variety of treatment processes to remove
contaminants from drinking water. These individual

processes may be arranged in a "treatment train" to remove undesirable
contaminants from the water. The most

commonly used processes include filtration, flocculation and
sedimentation, and disinfection. Some treatment trains

also include ion exchange and adsorption. A typical water treatment
plant would have only the combination of

processes needed to treat the contaminants in the source water used by
the facility. If you want to know what types

of treatment are used for your water supply, contact your local water
supplier or public works department.

Flocculation/Sedimentation 

Flocculation refers to water treatment processes that combine small
particles into larger particles, which settle out

of the water as sediment. Alum and iron salts or synthetic organic
polymers (alone, or in combination with metal

salts) are generally used to promote coagulation. Settling or
sedimentation is simply a gravity process that removes

flocculated particles from the water. 

Filtration 

Many water treatment facilities use filtration to remove remaining
particles from the water supply. Those particles

include clays and silts, natural organic matter, precipitants from
other treatment processes in the facility, iron and

manganese, and microorganisms. Filtration clarifies water and enhances
the effectiveness of disinfection.

Ion Exchange 

Ion exchange processes are used to remove inorganic constituents if
they cannot be removed adequately by

filtration or sedimentation. Ion exchange can be used to treat hard
water. It can also be used to remove arsenic,

chromium, excess fluoride, nitrates, radium, and uranium. 

Adsorption 

Organic contaminants, color, and taste- and odor-causing compounds can
stick to the surface of granular or

powdered activated carbon (GAC or PAC). GAC is generally more
effective than PAC in removing these

contaminants. Adsorption is not commonly used in public water
supplies.

Disinfection (chlorination, ozonation) 

Water is often disinfected before it enters the distribution system to
ensure that dangerous microbes are killed.

Chlorine, chloramines, or chlorine dioxide most often are used because
they are very effective disinfectants, and

residual concentrations can be maintained to guard against biological
contamination in the water distribution

system. Ozone is a powerful disinfectant, but it is not effective in
controlling biological contaminants in the

distribution pipes."

http://www.epa.gov/safewater/wot/wheredoes.html