I've used Omega pressure gauges for their extremely reliable operation, accurate pressure sensing and Arduino compatibility, but they are quite expensive. In particular I use this one to monitor the water level in a rainwater storage tank and it has worked perfectly for years: http://www.omega.com/pptst/PX309-5V.html
However if you just want to know if the pressure is below a certain value, a pressure switch like the one you linked is much cheaper and should be equally reliable. The pressure switches that are designed to control household well water pumps are mass produced and can be quite reasonably priced. For a (critical?) application like the water supply, you really need something that is designed to work without maintenance for years!
Finally, a switch designed for A.C. motors may not be reliable when used with an Arduino input. You may have to add a resistor to make sure that the switch carries some minimum amount of current, to ensure a good contact.