All water comes in the form of precipitation as water evaporates from the ocean by the energy of the sun at an overall rate of six feet of water each year. This water is salt-free and as the vapor rises being carried by the wind eventually condensing into the clouds. When the clouds become chilled the small particles of water collect into larger droplets which may very well precipitate over land or water.
As this water falls in the form of rain, snow, sleet or hail it clings to and carried with it dust and dirt that is in the air. Which means that the first precipitation that falls will inherit a considerable amount of contamination. Though after a short amount of time the water falling has presumptively less contaminants in it than the first precipitation does.
A large part of the evaporated water is carried onto land by the winds and the precipitation that falls helps to make up our fresh water supply. These droplets fall as rain may soak into the ground, fall as snow that lands on mountaintops melts and runs downstream or collect in lakes. However the droplets or precipitation falls eventually it all returns to the oceans, this is a generalization of how the hydrological cycle works.
Direct runoff :
Surface water accumulated mainly as a result of direct runoff from precipitation (rain or snow). Precipitation that does not enter the ground through infiltration or that is not evaporated back into the clouds is considered direct runoff. Direct runoff is water that drains from saturated or impermeable surfaces such as paved parking lots, etc. into stream channels or into natural or artificial storage sites.
The amount of water available on the surface depends largely upon rainfall. When rainfall is limited, the supply of surface water will vary considerably between wet and dry years. In areas of little rainfall such as California in recent years, people build cisterns for storage of rain, which drains from their roofs into roof gutter systems. This type of system can be very valuable in some areas such as Bermuda where groundwater is virtually non-existent and there are no streams. Many areas of the southern U.S. have adopted this type of water catch systems to aid in watering lawns, etc.
Surface water supplies may be further divided by river, lake and reservoir supplies. In general, they are characterized by soft water, turbidity, suspended solids, some color and microbial contaminants. Groundwater, on the other hand are characterized by higher concentrations of dissolved solids, dissolved gases, lower levels of color, relatively high hardness, and freedom from microbial contaminants.
Rivers and Streams:
Many of the largest cities in the world depend entirely upon large river for their water supplies. In using a river or stream supply one should always be concerned with upstream or river into which the treated wastewater (sewage) from upstream cities or towns has been discharged after being treated. This can present very serious problems in water treatment because of the upstream pollutants such as wastewater, agricultural drainage or industrial wastewater making the treatment of river or stream water very important.
River streams are also susceptible scouring of the bottom, changing channels and silting. Before the intake for a water supply is located in a river or stream, a careful study of stream bottom, its degree of scour, and settling of silt should be made. These issues should be considered before the intake of water into the treatment system to protect against floods, heaving silting, ice conditions and adverse runoff conditions. Because of these variants in the quality of water supplied by rivers or streams, purification effectiveness must be continually checked. This is especially true if there are industrial plants upstream from the intake which may dump undesirable wastes into the supply. Sudden pollutant loads might not be discovered unless constant monitoring of the raw water is maintained by the treatment plant operators.
Lakes and Reservoirs:
The selection and use of water from any surface storage source requires considerable study and thought. Where ponds, lakes or open reservoirs are used as a source of water supply, the danger of contamination and of the consequent spread of diseases such as typhoid, hepatitis, dysentery and giardiasis exists. Clear water is not always safe water and the old saying that running water purifies itself to drinking water quality within a stated distance is false.
In the fall, the cooler air temperatures cool the surface waters until it reaches the same temperature as the subsurface waters. At this point the water temperature is fairly uniform (the same) throughout the entire depth of the water supply. A breeze will blow which causes the surface water to circulate and thus cause the water to “turn over” thus bringing the poor water quality deeper to the surface.
Lakes, reservoirs, ponds are highly susceptible to algal blooms, especially after fall or spring turnover. The rapid growth of algae in the form of blooms will occur when the temperature is right and the water contains enough nutrients to support rapid algae growth. In any given body of water blooms of various types of algae can occur several times during the season depending on what algae is present and whether conditions are right for algae growth.
Water supplies drawn from lakes and reservoirs through multi-port intake facilities (openings at several depths) are in general of good quality since the water can be drawn from a depth where algae growths are not growing. A large lake or reservoir also dilutes any contamination that may have been discharged into it or one of its inflowing tributaries.
Large bodies of water are generally attractive recreation areas in many areas of the world. If the water is used for domestic supplies, however, it must be protected from contamination. This will require proper construction and location of recreation facilities such as boat launching ramps, boat harbors, and picnic/camping areas, fishing and open beach areas away from the intake area. The location and construction of wastewater collection treatment and disposal facilities must also be carefully studied to protect domestic water supplies from contaminants.
Part of the precipitation that falls infiltrates the soil, this water replenishes the soil moisture, or is used by growing plants and returned to the atmosphere by transpiration. Water that drains downward (percolates) below the root zone finally reaches a level at which the openings or voids in the earth are filled with water. This area is known as the zone of saturation, water in this zone is referred to as groundwater.
The upper surface of zone of saturation if not confined by material that will not allow water to flow through it is called the water table. When as overlying, impermeable formation confines the water in the zone of saturation under pressure. The name “Artesian” comes from the ancient province of Artesian in France where in the days of Romans, water flowed to the surface of the ground from a well. However, not all water from wells that penetrate Artesian formations flows to ground level. For a well to be Artesian, the water in the well must rise above the top of the aquifer. An aquifer or water bearing formation, is an underground layer of rock or soil that permits the passage of water.
The porous material just above the water table may contain water by capillarity in the small void spaces. This zone is referred to as the capillary fringe. Since the water held in the capillary fringe will not drain freely by gravity, this zone is not considered a true source of supply.
Because of irregularities in underground deposits or layers in the surface landscape, the water table occasionally meets the surface of the grounds at a spring or in the bed of a stream, lake or ocean. As a result, the groundwater is continually moves to these locations as seepage out of the aquifer (groundwater reservoir).
This groundwater is continually moving within aquifers even though the movement might be very slow thus, the water table may slope from areas of recharge to lower areas of discharge. The pressure difference represented by these slopes causes the flow of groundwater within the aquifer. Seasonal variations in the supply of water to the underground reservoir cause considerable changes in the elevation and slope of the water table and the Artesian pressure level.
Safe Drinking Water Act of 1974:
On December 16, 1974, the Safe Drinking Water Act (SDWA) was signed into law. The act set up a cooperative program among local, state and federal agencies with the Environmental Protection Agency developing the primary drinking water regulation designed to ensure safe drinking water for consumers.
A study of health effects of various contaminants in water supplies was begun soon after the signing of the SWDA. The regulations were developed in two stages so that the findings of this investigation and other studies could be incorporated into the regulations. The two stages were the interim regulations that became effective June 24, 1977 and they were followed by revised regulations.
All public water systems must comply with the regulations this includes all public or privately owned systems that:
1. Have at least 15 service connections, or
2. Regularly serve an average of at least 25 people at least 60 days out of the year.
Any water system that provides services for fewer connections or persons that this is not covered by SDWA. However, regardless of size, all operators must strive to provide consumers potable drinking water regulation. More types of contaminants must be monitored by communities than by non-community systems.
There are of course more regulations within the SDWA that can be found at your local library or on the Internet for your viewing pleasure. Things that separate industrial companies in some cases from community water supply systems where their demand is too high in comparison to the community itself in order to provide suitable supply to the entire community.
Factors affecting Water Quality:
Water quality within lakes and reservoirs is influenced and controlled by many factors. Of major concern is the fact that many conditions, which adversely affect water quality in domestic water supply reservoirs, result from man’s use of the environment. In order to control and maintain water quality, man’s activities must be controlled.
The occurrence of acid rainfall is of concern in both the United States and Europe. Pollutants from both motor vehicles and industrial plants has increased the acidity of rain in some areas to the point that when runoff reaches lakes and reservoirs, the biological balance is severely affected. Fish die-offs are obvious and easily detected but other biological upsets or trends may not be so obvious.
Wastewater, agricultural runoff, grazing of livestock, drainage from mining areas, runoffs from urban areas and industrial discharge may all lead to deterioration in physical, chemical or biological water quality within a reservoir. Increased turbidity and siltration may result from farming practices, fires and logging operations. If not properly controlled, public use of a reservoir may result in reduced water quality.
Natural factors which affect the quality of water in a given lake or reservoir include the following:
1. Climate temperature, intensity and direction of winds, type pattern, intensity and duration of precipitation.
2. Watershed and drainage areas: geology, topography, type and extent of vegetation and use by native animals.
3. Wildfires (caused by lightning, etc.)
4. Reservoir area: geology, land-form including depth, area and bottom topography, plant growth at the time the reservoir is filled.
Many water quality problems in domestic water supply reservoirs occur in reservoirs containing moderate or large quantities of nutrients such as phosphate, nitrate and organic nitrogen compounds. These nutrients may act as the stimulant to algae growth in the lake or reservoir just as they will stimulate the growth on a lawn, garden or orchard.
Tastes and Orders:
Objectionable odors and tastes in the domestic supply are often related to the occurrence of algal blooms. The nature of these tastes and odors is related to the particular type of algae but may change as the intensity of algal blooms changes. Some produce a grassy odor when populations are moderate, but more intense odor observed as a septic or pig pen odor when the algae populations are large, decaying or dying off. Costs increase when tastes and odors must be removed fortunately, many conventional plants are capable of reducing or eliminating tastes and odors when properly operated.
As you can see there are many factors, issues and concerns regarding the water supply issue as the precipitation yearly seems to decrease as water usage increases as well.