How do they build up so much pressure to push out through fire hoses, yet they do not have enough pressure to break the fire hydrant? Where does the pressure come from?
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Fire hydrants are made of thick steel strong enough to withstand the pressure from the flow of water. The same is true of all water pipes that connect to the hydrants (and every building that uses municipal water). The plumbing is designed by engineers to withstand the pressure found throughout the systems. Fire hoses are made of (typically) steel and nylon reinforced fabric over a rubber liner. They are narrower than the diameter of the hydrant pipe, so water pressure increases as it flows from a wider pipe to a smaller hose. The nozzles at the end of the hoses can further decrease the diameter of the water flow, increasing pressure even more. The pressure in the system is just the normal water pressure created by downward water flow (*i.e.*, gravity), supplemented where needed by water towers and possibly in-system pumps.
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