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Module 16: Water Distribution Systems

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Fonti di acqua, trattamento, distribuzione

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Sources of Water - Wells
Most of the drinking water comes from wells. Wells are sunk (dug, driven, drilled, or bored) into the earth to extract the water.

Click on each type of well to know more:
Shallow Wells
Wells that are dug or driven are considered shallow wells. These types of wells are generally used where the water table is within 20 to 50 feet of the earth’s surface. Dug wells are easily contaminated by surface water.

Driven Wells
Driven wells are made by forcing a well point into the earth. These wells are practical only where the soil is fairly free of rocks.

Deep Wells
Wells that are drilled are considered deep wells. They may extend hundreds of feet down through the earth. They are made using a drilling rig that penetrates subsurface materials.

Bored Wells
Bored wells are made using an earth auger (drill). Once the water table is reached and an adequate amount of water volume is found, a well casing is inserted to protect the well from contamination. Casings are made of various materials and depths, depending on how far the water is beneath the surface.

After the well is established, water is pumped to the surface to a storage tank inside or near the building, where it can be treated and used by the owners.

Reservoirs are made by building dams across rivers or streams. Municipalities can then collect and store water for future use.

Reservoirs are particularly important in areas that receive little rainfall for part of the year. A pump is used to move the water from the reservoir to the water treatment plant.

Treatment of Water
Much of the water from open reservoirs, lakes, streams, and some wells is not ready for human use until it has been treated.

Water must be tested for the presence of chemicals, turbidity (cloudiness resulting from suspended particles), organic materials, or other types of contaminants. Treatment removes impurities, odors, and unpleasant taste from the water.

Private water treatment often consists of a water softener. Depending on the hardness and quality of the water, some homes may have a sediment filter or carbon filter.

Municipal water treatment is more complex because of the high volume of water the general public uses. Millions of gallons of water must be treated in municipal water treatment plants each day to ensure an acceptable level of safety for the public.

Click on the following steps to know the sequence of how municipal water is treated in water treatment plants:

1
Water is pumped from a river or lake.

2
The water is sent to the aerators, where dissolved carbon dioxide is removed. The aerators also remove iron and manganese by oxidizing the minerals and filtering them out of the water.

3
The aerated water is then pumped to the clarifier, where lime and soda ash are mixed in to cause coagulation, or thickening, which removes precipitates of calcium and magnesium. Precipitates are deposits containing these elements. This process softens the water.

4
Carbon dioxide (CO2) is injected to re-carbonate the water and to stabilize and lower the acidity (pH) level. The water is then passed through rapid sand filters to remove any remaining particles.

5
After the filtering process, the water passes to the tanks, where a chlorine solution (sodium hydrochloride) disinfects it. At this stage, fluoride is usually added to reduce the chance of tooth decay. This treated water is then stored in reservoirs until needed.

6
After water leaves the treatment plant, it flows through pipes called water mains. The water mains usually run under the streets and serve many buildings. Permits are required to make connections to the water mains. The connections bring water from the main to the individual buildings through the building water service line.
Note:
In some areas, only municipal workers are authorized to make these connections. In other areas, licensed contractors or plumbers install the connections.

Supply and Distribution of Water
The water distribution system moves water from its source to the building or structure where it is needed. The way the water moves and the type of materials used can vary depending on the building or structure.

Private Water Supply
In a private water supply, the service line runs from the well to the house, and the pump can be located either at the well or at the house.

The installation of a private water supply system usually requires a well, although it may mean getting water from a spring or a cistern.

Note:
A private water source is required when access to municipal water supplies is not available, such as in rural areas.

A plumber may be responsible for setting (installing) the pump and completing the water service to the structure, or a certified well driller may do it.

Public Water Main
Water distribution and supply systems in buildings connected to the public water main differ from those used in private water supplies. Pumps are the primary distribution mechanism for buildings.

The building service line is tapped into the water main using a corporation stop. This is a valve that is threaded into the main without interrupting service to other locations.

The plumber runs the water supply piping from the curb stop to the building’s interior and installs a water line between the curb stop and the water meter connection.