The pressure applied to the water comes from a pump, you can place water in a pipe but unless you have some sort of pressure applied the water only flows to a lower point of gravity. It is the same with a balloon, as long as you blow into the balloon the balloon expands to accomodate the air pressure until the rubber reaches the breaking point then it bursts. You can also burst a water pipe if the pumping force is greater than the materials tensile strength, it happened in my washing machine hose the water pressure at my home is greater than the other homes going uphill so now I have to turn those hoses off until I use them. There has been several homes in my neighborhood on the downhill side that have had the bottom of their water meter explode because of the materials failure to hold all that pressure(from the waterpump and gravity applied to that because of downhill grade). Maybe this would be a good experiment for mythbusters to try at least it would be tamer than some others I have seen them do.