Mcmaster-Carr is an online store.  The solenoid is normally closed, so when you plug it in, the solenoid opens up (thus letting water through).  I currently have mine hooked up to a float switch.  If the water level in my sump gets too high, it trips the float switch and turns off the power to the solenoid, cutting off the freshwater supply. 
		
	
		
		
		
		
		
	
		
		
	
	
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