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map of proportion of population using improved drinking water sources in 2008
Proportion of Population by Country Using Improved Drinking Water Sources in 2008 Improved drinking water sources, e.g., household connections, public standpipes, boreholes, protected dug wells and springs, and rainwater collections, are defined as those more likely to provide safe water than unimproved water sources, e.g., unprotected wells and springs, vendor-provided water, bottled water (unless water for other uses is available from an improved source), and tanker truck-provided water. Source: World Health Organization

map of proportion of population using improved sanitation facilities in 2008
Proportion of Population by Country Using Improved Sanitation Facilities in 2008 Improved sanitation facilities, e.g., connection to public sewers or septic systems, pour-flush latrines, pit latrines, and ventilated improved pit latrines, are defined as those more likely to be sanitary than unimproved facilities, e.g., bucket latrines, public latrines, and open pit latrines. Source: World Health Organization

map of deaths by country from diarrhea caused by unsafe water, etc. in 2004
Deaths by Country from Diarrhea Caused by Unsafe Water, Unimproved Sanitation, and Poor Hygiene in Children Less than 5 Years Old, 2004 Source: World Health Organization

map of watersheds
Percentage of Impaired Water Bodies in a Watershed by State in USA Based on US EPA Data in 2000 Map of watersheds containing impaired water bodies from the U.S. Environmental Protection Agency's 1998 list of impaired waters Source: U.S. Geological Survey

Water chemistry overview

Compared to other molecules of similar molecular weight, water (H 2 O) has unique physical properties including high values for melting and boiling point, surface tension (water’s cohesion, or “stickiness”), and capacity to dissolve soluble minerals, i.e., act as a solvent    . These properties are related to its asymmetrical structure and polar nature , which means it is electrically neutral overall but it has a net positive charge on the side with the two hydrogen atoms and a net negative charge on the oxygen side (see Figure Structure of Water, Polar Charge of Water, and Hydrogen Bonds between Water Molecules ). This separation of the electrical charge within a water molecule results in hydrogen bonds with other water molecules, mineral surfaces (hydrogen bonding produces the water films on minerals in the unsaturated zone of the subsurface), and dissolved ions (atoms with a negative or positive charge). Many minerals and pollutants dissolve readily in water because water forms hydration shells (spheres of loosely coordinated, oriented water molecules) around ions.

Structure of water, polar charge of water, and hydrogen bonds between water molecules
Structure of Water, Polar Charge of Water, and Hydrogen Bonds between Water Molecules Source: Michal Maňas at Wikimedia Commons

Any natural water contains dissolved chemicals; some of these are important human nutrients, while others can be harmful to human health. The abundance of a water pollutant is commonly given in very small concentration units such as parts per million (ppm) or even parts per billion (ppb). An arsenic concentration of 1 ppm means 1 part of arsenic per million parts of water. This is equivalent to one drop of arsenic in 50 liters of water. To give you a different perspective on appreciating small concentration units, converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm to time units is 30 seconds in a year. Total dissolved solids (TDS) represent the total amount of dissolved material in water. Average TDS (salinity) values for rainwater, river water, and seawater are about 4 ppm, 120 ppm, and 35,000 ppm. As discussed in Module Climate Processes; External and Internal Controls , the most important processes that affect the salinity of natural waters are evaporation, which distills nearly pure water and leaves the dissolved ions in the original water, and chemical weathering, which involves mineral dissolution that adds dissolved ions to water. Fresh water is commonly defined as containing less than either 1,000 or 500 ppm TDS, but the US Environmental Protection Agency (EPA) recommends that drinking water not exceed 500 ppm TDS or else it will have an unpleasant salty taste.

Questions & Answers

the diagram of the digestive system
Assiatu Reply
How does twins formed
William Reply
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
what is genetics
Josephine Reply
Genetics is the study of heredity
Misack
how does twins formed?
Misack
What is manual
Hassan Reply
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
what is biology
Yousuf Reply
the study of living organisms and their interactions with one another and their environments
AI-Robot
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
Joseph Reply
what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
cell is the building block of life.
Condoleezza Reply
what is cell divisoin?
Aron Reply
Diversity of living thing
ISCONT
what is cell division
Aron Reply
Cell division is the process by which a single cell divides into two or more daughter cells. It is a fundamental process in all living organisms and is essential for growth, development, and reproduction. Cell division can occur through either mitosis or meiosis.
AI-Robot
What is life?
Allison Reply
life is defined as any system capable of performing functions such as eating, metabolizing,excreting,breathing,moving,Growing,reproducing,and responding to external stimuli.
Mohamed
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Source:  OpenStax, Sustainability: a comprehensive foundation. OpenStax CNX. Nov 11, 2013 Download for free at http://legacy.cnx.org/content/col11325/1.43
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