Most modern homes are equipped with copper piping for their water lines. Older homes in San Francisco don't have this luxury. If you live in a home that is over 100 years old it may have galvanized steel or, in the case of turn of the century homes, iron pipes. These pipes can be a major cause of high water pressure in a plumbing system. The interior of steel and iron pipes begin to corrode (most galvanized pipes only last 40 years) and collect mineral deposits on their interior walls. This creates higher pressure in some areas. The combination of thinned structural walls and high pressure can cause pipes to burst. A repiping with copper pipes can often prevent a major disaster.
While high water pressure may be a sign of problems in your pipes, low water pressure can be an indication that the interior of your piping is being eaten away. This is probably the case if you find you can't run more than one faucet at a time without losing considerable pressure. If you are having this problem, you probably also notice a distinct rust color in your water and a mineral taste. While you may not think too much of it, other than the discoloration that it leaves in the tub, you should think again. Galvanized steel piping contains lead which could be leeching into your drinking water. This is an extremely dangerous situation and should be handled immediately. If you are concerned about your water quality, contact a San Francisco plumbing contractor to check it for you.
Another viable option is PEX pipe. This flexible line is catching on due to its flexibility. This allows it to run longer distances without fittings or couplings. Using PEX to replace the older galvanized and iron pipes is cheaper than copper piping but it cannot be used outside. It also has an impermeable membrane that may lead to water contamination. If you are in a pinch, PEX may be the best choice for your indoor plumbing needs.