There are two general methods of supplying a building with water, one known as the "direct supply" system, and the other as the "indirect" or "tank" system.

In the direct system each fixture is connected with the supply pipe and is under the same pressure as the street main, unless a reducing valve is introduced. This system is not always desirable, as the street pressure in many places is likely to vary, especially where the water is pumped into the mains. A variable pressure is injurious to the fixtures, causing them to leak much sooner than if subjected to a steady pressure. Where the pressure in the street main exceeds 40 pounds per square inch, a reducing valve should be used if the direct system is to be employed.

Table VI. Capacity Of Cisterns, In Gallons, For Each 10 Inches In Depth

The following factors for changing a given quantity of water from one denomination to another will often be found useful:

Cubic feet X 62 1/2 = Pounds Pounds/ 62 1/2 = Cubic feet Gallons X 8.3 = Pounds Pounds/ 8.3 = Gallons Cubic feet X 7.48 = Gallons Gallons/ 7.48 = Cubic feet

For domestic purposes the indirect system is much better. In this case the connection with the street main is carried directly to a tank placed in the attic or at some point above the highest fixture, and all the water used in the house discharged into it. The supply of water is regulated by a ball-cock in the tank which shuts it off when a certain level is reached. All the plumbing fixtures are supplied from the tank, and are therefore under a constant pressure. This pressure depends upon the distance of the fixture below the tank. The pipes and fixtures in a house supplied with the tank system will last much longer and give much better results than if connected directly with the street main. The tank is also found useful for storage purposes in case of repairs to the street mains, which is often a matter of much inconvenience.

Fig. 7.

Fig. 7 shows the general arrangement of the cold-water pipes of an indirect supply system. On the right is shown the service pipe, which is carried directly from the street to the attic, and then connected with a ball-cock located inside the house tank. A supply pipe is taken from the bottom of the tank and carried downward through the building for supplying the various fixtures. A stopcock should be placed in the supply pipe for closing off the tank connections in case of repairs to the house-piping or fixtures.