Household Water By: Zoila Quiroz & Diana Chavez

Overview  Terms  Pascals Principle  Water Pressure  Water Tower, Pumps  How we get water into our home  Pipes  Experiment  Closing

Terms:  Pressure: defined by the equation Pressure = Force / Area  Units  The units of pressure are those of force divided by the units of area. The exact units depend on which system you are using  In scientific units force is measured in Netwons (1 N = 1 kg m / s2) and area in m2. Pressure has units of N/m2  In Imperial units force is measured in pounds and area in in2. Pressure has units of lbs/in2 (psi for short)

More Terms:  Atmospheric Pressure: Atmospheric pressure is the pressure exerted at the surface of a body by a column of air in an atmosphere. The pressure varies both with altitude, and weather patterns. Standard is an average atmospheric pressure at sea level, and is defined as 1 atmosphere on Earth, equal to 760 millimeters of mercury (760 Torr) and 101,325 Pascals. 1 atmosphere = 14.7 lbs/in2 = 101,000 N/m2 = bars = 760 Torr = 32 feet of water True Pressure: The total pressure exerted on a system equal to the gauge pressure and atmospheric pressure. Gauge Pressure: The pressure of a system measured by the gauge which excludes atmospheric pressure

Pascal’s Principle Pascal’s Principle: When a pressure is applied to a confined liquid, that a pressure is transmitted throughout the extent of the liquid.  Pressure exerted on an enclosed liquid is transmitted equally to every part of the liquid and to the walls of the container. (Pascal's principle)  A manometer relies on Pascal's principle to measure pressure in gases.  Pascal's principle is important in understanding hydraulics, the study of the transfer of forces through fluids.

Water Pressure  Water Pressure Explained  As we turn on the kitchen faucet or start a bath, how the water is coming out may not be something we think about. (Unless of course it is dripping or not coming out at all!) But, water pressure is something that we should all be familiar with. Most households receive water from a municipal water system. In this method, the water is usually extracted from various groundwater sources and then treated to remove impurities. Then, it is then pumped to water towers, where gravity takes over to provide the pressure that forces the water through pipes, and eventually to our homes. It is also important to note that water flow is not the same thing as water pressure.  As we turn on the kitchen faucet or start a bath, how the water is coming out may not be something we think about. (Unless of course it is dripping or not coming out at all!) But, water pressure is something that we should all be familiar with. Most households receive water from a municipal water system. In this method, the water is usually extracted from various groundwater sources and then treated to remove impurities. Then, it is then pumped to water towers, where gravity takes over to provide the pressure that forces the water through pipes, and eventually to our homes. It is also important to note that water flow is not the same thing as water pressure.  Water flow is the result of your water pressure on the amount of water available for delivery (volume). Low water flow could be a result of an obstruction on the water line, and old pipe with contain mineral build-up or corrosion that reduces the pipe’s internal diameter. So, if a water pressure gauge is reading at an acceptable level but the pressure seems off, it may be a flow problem.

How Do We Get Water in Our Homes?  Tower, Tank and Pump: A water tower is an incredibly simple device. Although water towers come in all shapes and sizes, they all do the same thing: A water tower is simply a large, elevated tank of water. Water towers are tall to provide pressure. Each foot of height provides 0.43 PSI (pounds per square Inch) of pressure. A typical municipal water supply runs at between 50 and 100 PSI (major appliances require at least 20 to 30 PSI). The water tower must be tall enough to supply that level of pressure to all of the houses and businesses in the area of the tower. So water towers are typically located on high ground, and they are tall enough to provide the necessary pressure. In hilly regions, a tower can sometimes be replaced by a simple tank located on the highest hill in the area. A water tower is an incredibly simple device. Although water towers come in all shapes and sizes, they all do the same thing: A water tower is simply a large, elevated tank of water. Water towers are tall to provide pressure. Each foot of height provides 0.43 PSI (pounds per square Inch) of pressure. A typical municipal water supply runs at between 50 and 100 PSI (major appliances require at least 20 to 30 PSI). The water tower must be tall enough to supply that level of pressure to all of the houses and businesses in the area of the tower. So water towers are typically located on high ground, and they are tall enough to provide the necessary pressure. In hilly regions, a tower can sometimes be replaced by a simple tank located on the highest hill in the area.

 In most towns, the water people drink comes from either a well, a river or a reservoir (normally a local lake). The water is treated in a water treatment plant to remove sediment (by filtration and/or settling) and bacteria (typically with ozone, ultraviolet light and chlorine). The output from the water treatment plant is clear, germ-free water. A high-lift pump pressurizes the water and sends it to the water system's primary feeder pipes. The water tower is attached to the primary feeders quite simply, as shown in this diagram:

 In a city, tall buildings often need to solve their own water pressure problems. Because the buildings are so tall, they often exceed the height that the city's water pressure can handle. Therefore, a tall building will have its own pumps and its own water towers.

Finally water arrives  Water supply  The water supply system brings cold water into the home under pressure. The water is piped in through a main supply line, usually from either a well, spring or municipal water supply. If the home has a water filtration or softening system it is most effective when positioned close to the point where the water supply enters the home. After entering the home, some of the water is immediately diverted to the water heater. At this point the hot and cold branch lines are run to stub outs for the various fixtures throughout the home. Small supply lines, are used to carry water from the stub outs to the fixtures.  The water heater is usually positioned close to the point where the main water line enters the home.

Pipes  Why Pipes Burst  When water freezes, it expands. That's why a can of soda explodes if it's put into a freezer to chill quickly and forgotten. When water freezes in a pipe, it expands the same way. If it expands enough, the pipe bursts, water escapes and serious damage results.  Surprisingly, ice forming in a pipe does not typically cause a break where the ice blockage occurs. It's not the radial expansion of ice against the wall of the pipe that causes the break. Rather, following a complete ice blockage in a pipe, continued freezing and expansion inside the pipe causes water pressure to increase downstream -- between the ice blockage and a closed faucet at the end. It's this increase in water pressure that leads to pipe failure. Usually the pipe bursts where little or no ice has formed. Upstream from the ice blockage the water can always retreat back towards its source, so there is no pressure build-up to cause a break. Water has to freeze for ice blockages to occur. Pipes that are adequately protected along their entire length by placement within the building's insulation, insulation on the pipe itself, or heating, are safe.

References:     FriedHoffer, BOB: Physics in the Home  Betts, John: Essentials of Applied Physics