Tanks and Sewer Line

Water Tanks

Proper storage of water is essential for various uses like bathing, cleaning, drinking, cooking etc. Water tanks are used to ensure safe and clean water for various purposes. So it becomes necessary to construct the tank in a way that maintains the purity and hygiene of water. In any building the provision for storage of is required to meet following requirements.

  • To maintain regular supply at the time of repairs of main water line etc.
  • To reduce maximum rate of demand on main water line.
  • To maintain regular supply at the time when supply is disturbed.
  • To store water for requirement of fire fighting.

Water tanks are constructed for storage of water. These are overhead and underground water storage tanks.

A water tank is a container for storing liquid. The need for a water tank is as old as civilization, to provide storage of water for use in many applications, drinking water, irrigation agriculture, fire suppression, agricultural farming, both for plants and livestock,


  • Chemical contact tank of DA polyethylene construction, allows for retention time for chemical treatment chemicals to “contact” (chemically treat) with product water.
  • Ground water tank, made of lined carbon steel, may receive water from a water well or from surface water, allowing a large volume of water to be placed in inventory and used during peak demand cycles.
  • Elevated water tank, also known as a water tower, will create a pressure at the ground-level outlet of 1 kPa per 10.2 cm or 1 psi per 2.31 feet of elevation. Thus a tank elevated to 20 metres creates about 200 kPa and a tank elevated to 70 feet creates about 30 psi of discharge pressure, sufficient for most domestic and industrial requirements.

Private well and pump systems include a well (the water source), piping from the well to the building, a water pump, and a water tank to which building water supply plumbing is connected. Building plumbing fixtures (sinks, toilets, showers, tubs) are supplied with water from the building water supply piping, and drain into the building drain-waste-vent (DWV) system.

Pressure tanks – When water is turned on at a fixture in the building, compressed air in the water tank acts like a spring: it pushes water out of the water tank and into the building water supply piping and thus water is sent on to the building plumbing fixtures.

If many fixtures are being run at once in the building, or if the water flow rate produced by the pump and piping and controls is a modest one, the pump may run continuously all while the fixture is being operated.

More typically, if only one fixture is running and if the pump and well can deliver a high water flow rate, the pump may come on and off several times while the fixture is being run.

As water leaves the water tank, water pressure in the water tank drops. Since the water tank also contains air, the air pressure drops too. In the tank water pressure and air pressure will be at the same psi. A pressure control switch, usually mounted on or near the water tank, senses the pressure drop, and at a pre-set “pump cut-in pressure” (typically 20 or 30 psi) the pressure switch turns on the water pump. The water pump, located at the tank or perhaps in the well, pumps water to the building from the well, simultaneously re-pressurizing the water tank and providing water to the building. Because the water pressure tank is connected to the water pump (water in from the well) and also to the building water supply piping (water out to the building) the water tank is said to be “floated on the water line” and when the water pump is running water is pushed simultaneously into the water pressure tank and into the building supply piping.

Overhead tank should be constructed nearest to fittings through which the water is supplied so that long horizontal length of GI pipes could be avoided. The tank should be constructed 30 to 45 cm from the terrace to provide easy cleaning under storage tank. All fittings such as supply pipes, distribution pipes, over flow pipes, and air vent pipes should be fixed during construction of wall for water tank. No hole should be drilled after completion of construction. If it’s done, leakage problems may occur. Use vibrated cement concrete in 1:1.5:3 ratios for top and bottom slab. The slab and sides of water tank should be plastered and rendered with cement slurry to avoid leakage. Proper over flow pipe should be fixed and be connected to the rainwater pipe. Ball valve /Ball Cock should be fixed in the tank to avoid the problem of overflow. Curing of RCC, brick work and plaster should be done for minimum period of 7 to 10 days.

Under Ground water Storage Tank

  • Underground storage tank should be 30 cm above highest flood level or ground level whichever is higher.
  • The top of tank should be at such level that prevents entry of outside water from ground or floor.
  • The water should not be allowed to stand around the tank.
  • The tank should be constructed in such way that provides easy cleaning of the tank when required.
  • For cleaning purposes the floor of the tank should be laid with slope at one corner where the water can be pumped out for cleaning the tank.
  • The tank should be perfectly water tight.
  • The inner surface of the tank should be rendered smooth.
  • All fittings such as supply pipes, distribution pipes, over flow pipes, and air vent pipes should be fixed during construction of wall for water tank.
  • No hole should be drilled after completion of construction. If it’s done, leakage problems may occur.

Sewer Line and Drainage

Sewerage and drainage systems are used to carry waste from building to public sewer system. Where public sewerage does not exist, the disposal is made into septic tank, socking pits etc. (Individual disposal system). The following are systems of sewerage and plumbing.

Sewerage System

  • Combined Sewerage System – It’s a system in which the foul water (sewage) and surface water is carried through same sewers and drains.
  • Separate Sewerage System – It’s a system in which the foul water and surface water is carried through separate sewers and drains.
  • Partially Separate Sewerage System – It’s a system in which a part of surface water is carried through foul sewers and drains.

Waste Water Pipes – Waste water pipes maintain proper hygienic conditions in any building. They are used for proper outlet of waste water from the house. The pipes prevent home from foul smell of waste water also. There are various types of pipes available in the market to ensure sanitary conditions in any structure. Here we have enlisted the types of pipes for proper drainage of waste water.

Types of Waste Water Pipes

  • UPVC Pipes – These UPVC pipes are used as waste water pipes for drainage purpose and have a superior intensity and working pressure. They are environmentally safe, chemical resistant and provide lasting quality. They are economical and easy in installation. They provide perfect water tightness.
  • Clayware Pipes – Clayware waste water pipes are convenient in handling and layout. They have rigid fittings and do not distort under loading. They maintain good corrosion resistance.
  • The pipes provide flexible joints at sufficient and frequent intervals.
  • Fiber Cement Pipes – These type of waste water pipes are resistant to corrosion and maintain qualities of both concrete and inorganic fiber. They have a service life of minimum 50 to 75 years and do not create any problems in storage. They remain unaffected in strength by high temperatures and maintain thermal conductivity approximately 120 times less than metal pipes. They have smooth bores and low friction losses. Fiber cement pipes maintain their carrying capacity during service period. These waste pipes improve with the passage of time and yield to better test results in terms of strength when kept in humid environment. The ends of pipes can be turned into accurate dimensions. The pipes can be drilled, cut, turned at the site of job by handy tools.
  • Concrete Pipes – These pipes are environment-friendly and provide structural strength. These are generally used for carrying the waste water from the sewer line. They are resistant to abrasion and most chemicals. They are easy to install and have a history of reliability. The pipes get stronger with the passage of time and life cycle of a steel reinforced concrete pipe is considerably longer than other drainage pipes.
  • Ductile Iron Pipes – These pipes are chemical resistant and have high tensile strength. These waste water pipes are best suitable for carrying the industrial waste. These are also resistant to second cover damage. They are economical and easy in installation. They are not damaged while handling or during transportation. They have high elongation (ductility).

The diameter of waste water pipes should be based on fixture units. Branches and piles receiving discharges from soil appliances should not be less than 100 mm diameter. Outlet of floor traps may be of 75 mm diameter. Waste stack should have a minimum diameter of 75 mm.

Various colors indicating Sewer, Waste and Water Pipes

  • Red color indicates sewers.
  • Blue color indicates waste water pipes.
  • Blue color marks rain water pipes also.
  • Black color marks existing works.

Sanitary Drainage

In a multi-story building such as a condominium complex, the sanitary drainage system consists of three main components – vertical stacks, branch lines and horizontal underground lines.

Types of Vertical Stacks – Stacks are vertical lines of pipe that extend from the horizontal building drain under the slab or in the basement up to and through the roof of the building. Although the general direction which these pipes run is vertical, they may be offset or run in a horizontal position on upper floors and still be identified as a vertical stack. In the industry these pipes are either known as soil stacks, waste stacks, or vent stacks depending on the purposes which they serve.

Soil Stacks – The distinguishing factor that gives soil stacks their name is that they receive discharge from water closets and urinals. Clean water fixtures such as sinks and showers may also tie into soil stacks.

Waste Stacks – Waste stacks are tied into clean-water fixtures only – such as sinks, showers, bathtubs, lavatories, and the like. Waste stacks never receive waste from fixtures such as water closets or urinals. If a fixture such as a water closet or urinal was ever tied into a waste stack, it would thereupon become a soil stack.

Vet Stacks – Vent stacks carry no liquids. Their role is to provide airflow through the drainage system so that when water flows through branches and stacks the traps will not be forced by back pressure. The portion of a vertical stack that is above the highest fixture tie in becomes a vent stack.

Leaders – Rain leaders are vertical stacks in that they extend from the horizontal storm drain or combined sewer drain to the roof. They are called rain leaders because they transport rain water only.

Branch Lines – Branch Lines are offshoots of vertical stacks, like branches of a tree. These branch lines connect toilets, showers, sinks, washing machines, dish washers, etc. to the corresponding vertical stack, which carries waste to the building’s drain underground or in the basement.

Horizontal Underground Lines – Horizontal Lines run underneath the building’s slab, often under common areas such as the lobby and individual ground floor units. These lines are typically 6-8″ in diameter depending on the size of the building. Since sanitary drainage is gravity powered, underground main lines are slightly pitched to carry waste away from the building into the city sewer. The horizontal pipe that receives discharge from waste and soil stacks and is located within the buildings footprint is called the “building drain” and thereafter is known as the “building sewer”.

Common Types of Pipes in Building – The most common pipe used in sanitary drainage in older buildings is cast iron. Next up is clay. Newer buildings however, are often built with PVC. Here is a brief overview of these different piping materials.

Cast Iron Pipes – Cast iron sewer pipes have a life-use expectancy of 25-35 years and then they begin to develop cracks and channels. Cast iron piping is still by far the most common material used for sanitary drainage in multi-story buildings such as condominiums and apartment buildings.

Here are some key advantages of cast iron pipe that come into play:

  • Cast iron drainage pipes offer durability and can support 4,877 lbs per linear foot.
  • Cast iron piping reduces noise due to its density, which is an important selling point for condominiums, apartment buildings and hotels.
  • Fire-resistance is another key factor of cast iron pipes as they will neither burn or contribute to the spread of fire.

The main disadvantages include:

  • Cast iron piping is expensive.
  • Cast iron has a relatively short lifespan of 25-35 years (in South Florida).

After cast iron’s expected life-use of 25-35 years, the pipes can be expected to begin developing channels in horizontal lines and cracks in both horizontal and vertical lines. Buildings in close proximity to the ocean experience accelerated cast iron pipe deterioration due to the salt in the air which is pulled down the vent stacks and the fact that the underground cast iron pipes are often submerged in salt water twice a day with high tide. Salt and cast iron is a corrosive combination. Cast iron piping, however, is often still favored over PVC in condominium applications due to the advantages listed at the outset.

Vitrified Clay Pipes – Vitrified clay piping dates back to 4000 B.C.E., however is rarely used today. Clay sewer pipes are most common in historic homes and buildings. Vitrified clay sewer pipes have been in use since ancient times with the earliest known example dating back to Babylonia, 4000 B.C.E.

Advantages of vitrified clay piping include:

  • Durability
  • Chemical resistant material for sanitary drainage

However the disadvantages of clay pipes include:

  • Clay is very susceptible to tree root intrusion as the porous outer surface is easy for roots to attach to
  • Very heavy and hard to cut
  • You most likely will not find it in your neighborhood home improvement store.

PVC Piping – Studies suggest that PVC pipes have a service life of 100 or more years. Starting in the 1970’s PVC pipes began to be installed in mass quantities. Cast iron proponents would say that not enough time has yet elapsed to determine the service life of PVC, however, studies suggest a 100-year or more lifespan for PVC. PVC versus Cast Iron has been a hot topic in the pipe manufacturing industry for years. However certain advantages are clear and include:

  • Longevity
  • Cost efficiency

However certain disadvantages are clear as well and include:

  • Non fire-resistant, additional fire-stopping measures required upon installation.
  • Carcinogenic fumes when exposed to excessive heat.
  • Not as strong as cast iron.
  • Noisy water transportation (not ideal for multi-story residential buildings such as condominiums and hotels).

Septic Tank

Septic tanks or soak pits are useful for disposal of waste in the areas or houses where public sewerage system is not applicable. Public sewerage system is not laid at some places or in houses located in isolated areas which cannot be connected with public sewer system economically. In this situation the waste of the house can be disposed-off through individual disposal system such as septic tank or soak pit etc. Septic tank has limitations and will provide unsatisfactory quality of the effluent and also faces difficulty for providing proper disposal system of the effluent. The septic tank is recommended for small communities where population does not exceed 300.

Sewage and waste of the house come into septic tank and solid matters settle down at the bottom of the tank. Anaerobic Bacteria convert the sewage into liquid and gases during the process of digestion. In this way there is appreciable reduction in the volume of waste and it changes into semi solid condition, which is called sludge. It is necessary that septic tank is covered with water tight top roof slab. Septic tanks are generally constructed in brick masonry.

Guidelines for Septic Tank

  • Sufficient water is required for proper functioning of septic tank.
  • The waste containing detergent should be avoided in septic tank as it had adverse effect on anaerobic bacteria.
  • Septic tank should have minimum width of 0.75 meter and minimum depth of 1 meter below water level of the septic tank.
  • Length of the tank should be 2 to 4 times the width.
  • Every septic tank should be provided with ventilation pipe of at least 50 mm diameter.
  • Minimum free board above water level should be of 30 cm.
  • The floor of the tank should be of cement concrete 1:1.5:3 and has a minimum slope 1 in 10 provided towards the sludge outlet to facilitate de-sludging.
  • The inner surface of septic tank should be plastered with rich cement.
  • For efficient working of septic tank the sludge should be cleaned half yearly or yearly.

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