Part III reviews the sources of water available for potable water and irrigation water.
Many common water resource terms will be explained but you can go to the Water Lingo Tab for more definitions and information. Reference photos are provided of waterworks facilities constructed and/or managed in CT, IL and CA. Notes  containing supplemental information are provided at the end of the blog.
Precipitation via the water cycle is the origin of water resources. See diagram below.
Precipitation in the form of rain or melted snow ultimately becomes either (1) groundwater or (2) surface water.
Precipitation percolates down through the ground into a layer of water-bearing unconsolidated materials (gravel, sand or silt) called an aquifer.  The top of the saturated portion of the aquifer is called the water table. Groundwater is water derived from an aquifer.
Groundwater is removed from the aquifer via a pump inside a well. See diagram above. A well is a long cylindrical steel casing installed in a vertical hole drilled in an aquifer. The bottom of the casing is screened to allow groundwater to enter the casing. See well screen photo (left).
A well pump is installed inside the well. The pump can be vertical turbine (motor is above ground as shown in the diagram and photo-right) or submersible (sealed motor is installed in the well and coupled directly to the pump). 
Aquifer provides a natural storage reservoir for natural groundwater recharge (precipitation) and artificial groundwater recharge (surface water or reclaimed/recycled wastewater).
Groundwater is naturally filtered (cleaned) as it travels through the unconsolidated sand & gravel layers into the well/pump. Complex water treatment may not be required.
Aquifers are not uniform and portions of the aquifer may not have good transmissivity, i.e. unconsolidated materials are "tight" and may not allow groundwater to flow easily.
Aquifers may contain sediments with high levels of natural harmful minerals that can dissolve into groundwater and render groundwater unusable or require complex water treatment, e.g. chromium and arsenic.
Aquifers can become subject to man-made pollution and render groundwater unusable or require complex water treatment, e.g. petroleum and solvents.
Aquifers are hard to manage because they are below the earth's surface and not visible--making monitoring difficult.
Groundwater overdraft (groundwater withdrawal exceeds natural and artificial recharge) can cause land subsidence. Land subsidence can result in structural, roadway and utility infrastructure damage. See example of land subsidence due to groundwater overdraft in San Joaquin Valley, California below.
Precipitation that does not percolate deep into the ground (moves across impervious surfaces like clay, rock, pavement, etc.) will find its way to a stream, river or lake which are surface waters.
Use of surface water is very common in the non-arid portions of the US. Usually streams or rivers are impounded by dams which create a water body (lake) where surface water is removed via an intake. The intake transfers the surface water to a potable water system or irrigation system. Below are photos of the Alton (IL) Water Treatment Plant and Intake on the Mississippi River constructed in 2003 (just upstream of St. Louis and the Melvin Price Locks & Dam).
In arid regions, rivers and streams are typically ephemeral (intermittent flow) and cannot be used as a reliable water supply. The Tucson region has many ephemeral streams/rivers (aka dry washes) that only flow during a precipitation event.
The only big exception is the Colorado River which has a huge watershed, capturing precipitation in the Upper Basin states (Wyoming, Colorado, Utah and New Mexico) and flowing south through the thirsty arid Lower Basin states (Nevada, Arizona and California). If not for the Colorado River, growth in the Lower Basin states would be minimal. The Colorado River will be covered in more detail in future Know Your H2O blog(s).
Surface water is easier to manage because you can physically see it and readily monitor quality and quantity.
Some surface waters can provide huge volumes of water, e.g. Colorado River, Mississippi River, etc. The roadblock is constructing the massive transportation infrastructure to get that water to areas of need.
Surface water is subject to flooding and drought. Surface water facilities must be planned and designed to accommodate a wide range of natural events. For example, large man-made storage reservoirs may be required to store surface water during wet periods for use during dry periods.
Surface water will contain sediment, biological and other contaminants that will require treatment for potable use and minor treatment for irrigation use. 
Surface water can become subject to man-made pollution and render surface water unusable or require additional complex water treatment, e.g. petroleum and solvents.
So there you have it! Seems simple enough, but as pointed out in the pros/cons, utilizing groundwater and surface water for potable water and irrigation water can get very complex.
Next up--Arizona Water Law.
 Fractures and voids in underground rock deposits can also yield groundwater but is usually very limited. Rock wells are common in northern New England.
 Most wells are housed in a small structure to protect the equipment from the elements and provide added security. The well in the photo is located in warm/sunny La Quinta, CA where freezing is not a problem.
 Ocean water is also a surface water and can be utilized as a potable water or irrigation water source but it requires desalination treatment which is extremely expensive and creates a brine waste. The treatment cost, waste handling cost and the transportation infrastructure cost to get ocean water to the Tucson area eliminates ocean water as an economically viable water source.
 All surface waters in the US require filtration treatment for potable use. The only exception is the Catskill and Delaware water supplies for New York City which have a waiver due to their expansive, pristine watersheds. Surface water used for irrigation usually requires minor treatment to reduce sediment.