Municipal water supply systems
Water is vital to everyday life, and throughout history people have devised
systems to make getting and using it more convenient. Early Rome had indoor
plumbing, meaning a system of aqueducts and pipes that terminated in homes and
at public wells and fountains for people to use.
Modern water supply systems get water from a variety of locations, including
aquifers, lakes, rivers, wells, desalinated seawater, and other sources. The
water is then purified.
The intake from these water sources usually is through a large cage-like box
designed to screen out large particulate matter before it enters the system.
After it is sucked in by a pumping station or allowed in by a gravity-feed
system, it is usually filtered further, chlorinated, fluoridated, and then
pumped either to holding locations like water towers or reservoirs, or fed
directly into the user's spigot.
Municipalities typically run water supply systems, although sometimes this is
the job of a regional supplier that has an independent governmental structure
and taxing authority.
Once water is used, it has to go somewhere. Typically wastewater is piped away
in a sewer system, which is again almost always a service provided by the same
authority as the water supply, since usage of one system implies usage of the
Sometimes, due to contamination by pathogens which exceeds a municipality's
ability to filter and purify its water supply, a boil water advisory may be
Examples of water supplies
In the city of Highland Park, Illinois, the water source is Lake Michigan. A
large pipe extends out into the lake to a large concrete and metal structure on
the lake bottom which acts as the intake filter. This filter screens out only
the largest of debris, including wood or large rocks. A set of large electric
submersible pumps in a pumphouse building on the shoreline sucks the water into
a system of sand and other filters to screen out large and small debris,
including fish, leaves, or gravel. The water then is pumped through a set of
pipes where it is chlorinated to kill bacteria, viruses, and any small
multicelled organisms that manage to make it through the filters. The water is
then fluoridated to benefit public dental health. Finally, the water is tested
by various sensors to determine if it is safe to drink, and pumped to higher
locations. In this case, the higher locations are water towers situated around
the town. These water towers provide water pressure to prevent leaks in the
system from allowing untreated and unsanitary groundwater from entering the
system. This also has the benefit of providing a constant water pressure to the
town, achieved by the height. Water pipes lead to almost every house and
business in town, as well as to fire hydrants. Water pipes enter each building
and (once inside to prevent damage from freezing weather) there is a water meter
to track water usage. From there, it is piped through the building to the sinks,
water heater(s), toilets, showers, garden hoses, and other usage points. Water
costs about $1 per 100 cubic feet (2.8 m³).
In the city of Lawrence, Kansas, the water source is the Kansas River. A small
dam in town provides electricity and has a water intake for the water treatment
plant. Like Highland Park, above, the water is filtered, chlorinated,
fluoridated, pumped to water towers, and used.
In the city of Cottage Grove, Oregon, the water source is a large reservoir, a
specially designed, built, and maintained lake, on a mountainside above the town
which provides water pressure. The water is filtered, chlorinated, fluoridated,
and delivered through town.
As late as the 1960's, the water supply pipes buried through town were made of
wood, which is the source of the name "Trunk Main" used when describing larger
bulk-water transfer mains, due to the large timber industry and ready
availability of wood as a construction material. These were later replaced with
concrete, steel, and PVC pipes. This work was delayed because it takes a lot of
water to equal the cost of digging up a leaky pipe with expensive construction
equipment and replace it with better pipes.
Constant pressure in the water supply system is necessary to keep the water
flowing through the system. Pressure in an urban water system is typically
maintained either by a pressurized water tank serving an urban area or by
pumping the water up into a tower and relying on gravity to maintain a constant
pressure in the system. Water pressure due to gravity is approximately 42 pounds
per square inch (psi) (290 kPa) per 100 feet (30.5 m)of elevation. Thus, if the
level of water in a water tower is 100 feet (30.5 m) above ground level, the
pressure in the system would be 42 psi (290 kPa); a 150-foot (45.7 m) tower
would produce pressure of 63 psi (434 kPa). Water pressures vary in different
locations and water mains below the street may operate at higher pressures, with
a pressure reducer located at each point where the water enters a building or a
Water Filters -