Check the water pressure entering your home; it should be 40 - 100 pounds per square inch (psi). If the incoming pressure is OK, corrosion, sediment, or mineral buildup in galvanized pipes may be the problem. Horizontal lines and hot-water pipes are most prone to clogs. However, any galvanized pipe can clog.
The ultimate solution is to replace old plumbing with copper pipes -- a time-consuming and expensive job. Here are several simple solutions. The method shown will clear pipes but can also clean corroded joints where sediment alone was preventing leaks. Use compressed air gently. Clear pipes between a faucet and the water heater, then use the same method to clear pipes from the water heater to the main shutoff. Don't blast compressed air through a water heater -- you could damage its lining.
Several hours to assemble the parts and to force out sediment with an air compressor
Pipe wrenches, groove-joint pliers, air compressor, hand-crank auger, wire cutters, toothbrush
Dismantling and assembling galvanized steel pipe
Determine which pipes are clogged; map where the pipes run.
Parts to connect an air compressor to a pipe, pan or bucket, perhaps new aerators
If water flows slowly at one faucet or appliance only, chances are that an aerator or a screen is clogged. At a washing machine, shut off the hose valve and disconnect the hoses from the back of the machine. Pry out the screens in the machine's inlets or hose ends and clean them.