290
Potable water is transported locally and not over long distances, for multiple
reasons. It is difficult to maintain constant system pressures across long distances.
Water quality degrades over time and distance. Most importantly, the institutions
that operate the potable water infrastructure rarely cross municipal or property
boundaries. Potable water is critical infrastructure because it is essential for human
life and for nearly all economic activities. This means reliability of supply is
extremely important. Demand for potable water in cities varies strongly by time of
day and time of year. Peaks in residential demand occurring at the start and end of
the workday as people wash and cook, and peaks in commercial demand occur during the workday, with low demands at night. Because potable water is used for
landscaping and outdoor water use in cities, demand also peaks during the warm
season and growing season when plants need more watering. If a fire starts, the
system must deliver extremely high rates of supply for 1 or 2 h. In order to match
supply with demand at all times of day and year, and to ensure reliable supplies during temporary failures of electrical power, pumps, or unavailable or contaminated
source water supplies, potable water systems incorporate storage. Usually there is
between 24 h and 5 days of storage.
Because water supply uses a large fraction of electrical power demands (USGS),
a best practice is to produce potable water and treat wastewater at times of day when
electricity is inexpensive, and use stored potable water at times of day when electricity is expensive.
Potable water is easy to store in large steel tanks. Elevated storage is a best practice, because it can maintain system pressures in the absence of electrical power or
functioning pumps, and it is provided by placing storage on hills or in water towers.
Potable water distribution works on zones that distribute treated water from one
or more water treatment facilities to one or more users. A zone operates at a fixed
positive pressure that is high enough to provide strong flow rates. A zone is a grid or
network of small pipes that are connected together in a series of loops and junctions.
Positive system pressures result in leakage, which is usually less than 5 percent in a
well-maintained system, but can be 30–50 percent in the oldest systems. The distribution system’s design is usually limited by the dual purpose of firefighting, which
has much higher peak demands, rather than by residential and business uses.
Wastewater distribution is usually run by gravity (downhill) where possible, using
traditional sewer designs.
The soft infrastructure of potable and waste water systems is comprised of consumption, ownership, finance, and governance.
Potable water is used for drinking, sanitation, outdoor landscaping, firefighting,
construction, social & lifestyle, and most industrial processes, in residences and
businesses, especially in cities. Potable water is an essential and non-substitutable
input into nearly all economic processes, and especially for human life and residential uses.
Cities cannot exist without high quality potable water supplies and wastewater
services, and this fact has held constant for the entirety of human civilization.
Potable water systems are owned by water utilities, which are publicly regulated
B. L. Ruddell et al.
Potable water is transported locally and not over long distances, for multiple
reasons. It is difficult to maintain constant system pressures across long distances.
Water quality degrades over time and distance. Most importantly, the institutions
that operate the potable water infrastructure rarely cross municipal or property
boundaries. Potable water is critical infrastructure because it is essential for human
life and for nearly all economic activities. This means reliability of supply is
extremely important. Demand for potable water in cities varies strongly by time of
day and time of year. Peaks in residential demand occurring at the start and end of
the workday as people wash and cook, and peaks in commercial demand occur during the workday, with low demands at night. Because potable water is used for
landscaping and outdoor water use in cities, demand also peaks during the warm
season and growing season when plants need more watering. If a fire starts, the
system must deliver extremely high rates of supply for 1 or 2 h. In order to match
supply with demand at all times of day and year, and to ensure reliable supplies during temporary failures of electrical power, pumps, or unavailable or contaminated
source water supplies, potable water systems incorporate storage. Usually there is
between 24 h and 5 days of storage.
Because water supply uses a large fraction of electrical power demands (USGS),
a best practice is to produce potable water and treat wastewater at times of day when
electricity is inexpensive, and use stored potable water at times of day when electricity is expensive.
Potable water is easy to store in large steel tanks. Elevated storage is a best practice, because it can maintain system pressures in the absence of electrical power or
functioning pumps, and it is provided by placing storage on hills or in water towers.
Potable water distribution works on zones that distribute treated water from one
or more water treatment facilities to one or more users. A zone operates at a fixed
positive pressure that is high enough to provide strong flow rates. A zone is a grid or
network of small pipes that are connected together in a series of loops and junctions.
Positive system pressures result in leakage, which is usually less than 5 percent in a
well-maintained system, but can be 30–50 percent in the oldest systems. The distribution system’s design is usually limited by the dual purpose of firefighting, which
has much higher peak demands, rather than by residential and business uses.
Wastewater distribution is usually run by gravity (downhill) where possible, using
traditional sewer designs.
The soft infrastructure of potable and waste water systems is comprised of consumption, ownership, finance, and governance.
Potable water is used for drinking, sanitation, outdoor landscaping, firefighting,
construction, social & lifestyle, and most industrial processes, in residences and
businesses, especially in cities. Potable water is an essential and non-substitutable
input into nearly all economic processes, and especially for human life and residential uses.
Cities cannot exist without high quality potable water supplies and wastewater
services, and this fact has held constant for the entirety of human civilization.
Potable water systems are owned by water utilities, which are publicly regulated
B. L. Ruddell et al.