The great fire of 1906 was caused by the fact that the water mains leading into the City, lying in filled-in and loose earth, had broken as the result of an earthquake. When several fires started simultaneously in different sections of the City, as the result of decrepit buildings having fallen down, the water in the pipes was soon exhausted by the fire engines. The City was then at the mercy of the flames.

A study of the earth’s fault lines by scientists disclosed that any system of pipes leading up the peninsula would have to cross some of these faults and that at another earthquake the mains might again be broken. With this in mind, the engineers determined that a sufficient amount of water should always be in readiness in the City itself to take care of any fire or fires that might be started as the previous one was.

It was therefore determined to build an entire system of mains independent of the regular water system, for the fighting of fires, and that this system should be supplied from a reservoir, high up over the City, so that no engines would be necessary for pumping. This was to be known as the High Pressure Water System.

It was also determined that this high pressure system should be connected with the bay, so that if by any chance the system should be cut off the reservoir, saltwater could be forced into the system for the purpose of fighting a conflagration.

In addition to these precautions it was determined to install and extend the system of cisterns throughout the City so that the Department, if driven to this last recourse, could always find a sufficient amount of water to find any ordinary fire. In the great fire of 1906 it was impossible for the Department to get even enough water to fill the boilers of the engines to generate steam. With the present motor-driven engines, of course, water for this purpose would not now be needed.

To provide for this independent high pressure system a bond issue of $5,200,000 was voted by the people. By reason of premiums on the bonds sold and interest earned during the building of the system the City realized about $6,000,000.

With this money the City built a reservoir on the Twin Peaks at the altitude of 758 feet. Water from this reservoir will go to the top of the highest buildings in the City through the standpipes that run up the sides of them. This reservoir has a capacity of about ten and one-half million gallons of water and is kept filled at all times.

From this reservoir a system of mains leads first to two regulating reservoirs. One, known as the Ashbury tank, is of steel and contains 500,000 gallons of water at an altitude of 465 feet.

The second of these reservoirs is known as the Jones-street tank, which is built of reinforced concrete at an altitude of 339 feet and contain 750,000 gallons of water.

From these three reservoirs a system of mains radiate throughout the business section of the City. This district is contained in what is known as the fire limits. As these limits are extended and the high pressure mains laid, all buildings thereafter constructed must be of fire-proof construction. There have now been laid approximately 74 miles of high pressure mains. Twenty inches in diameter is the largest of the pipes, which are of heavy construction, the smallest being ten inches, with an eight-inch lead from the main to the hydrant.

Taking a lesson from the Pioneers and their construction of cisterns, fifty-four of the old cisterns built as far back as 1860 were repaired and placed in service. In addition to these eighty-five new reinforced concrete cisterns were built, making a total of 139. The new cisterns were built to contain 75,000 gallons each, while the old ones, built of brick contain varying amounts of from 32,000 gallons to 90,000 gallons. These cisterns and the three large reservoirs are kept filled from the local water company’s mains.

In order to provide for the use of saltwater from the bay, in case the water in the higher reservoirs could not be used, two pumping stations were built on the bay shore. One is known as the Ft. Mason pumping station or pumping station No. 2, and the other is located on the northwest corner of Second and Townsend streets, known as pumping station No. 1. These stations contain electrically driven machinery which at a moment’s notice can begin pumping saltwater into the high pressure system. If necessary this water can be forced from the bay right up to the Twin Peaks reservoir; or, by closing of valves, the water can be directed through the mains in any desired direction.

One other important unit was added to the City’s fire fighting system out of this $6,000,000; this was that of two fire-boats, one known as the Dennis Sullivan and the other David Scannell. These two boats can pump 10,500 gallons of water a minute each. They are twin boats and can discharge twenty-five streams of saltwater. These boats can be attached to pipes at different places along the wharves and their pumps can be used to supply water for fires several blocks inland through hose connections. But their main use is for fire in ships and along the docks. and they have rendered great assistance on many occasions at other cities and towns about the bay.

It is believed that with the precautions the City has so fortified itself that no great fire can ever again devastate the City.