How to connect Onion Omega relay board to AC110V Electric Solenoid Valve
The relay board says it will handle 60W (one or both- it's not really clear); the solenoid valve says it takes 18W. 

As such it appears it should work. 

It's a good idea to put a MOV (Varistor) or bidirectional TVS across the solenoid coil rated for the AC voltage used (so at least 200V peak DC voltage). For example, a P6KE250CA, because the high inductance of a solenoid valve coil will cause a lot of contact sparking and electrical noise. 

Generally relays rated at only 2A are not really intended to switch that kind of load and have a life that is very many operations, but there's no real information what the actual relay rating is, only the board (so the relay may be derated).