Come on now! Just why are you referring to this particular wire which is intended for a completely different purpose!
Looking for the cheapest option is not necessarily a sensible idea, certainly not if you lack the important design skills. It should be obvious that you need two wires for a start, and related to Klaus' comments, you should be using a twin or "figure eight" cable. You could twist two runs of the wire you cite, together to achieve that but it may not be as sturdy as you might wish.
You really need to explain how you propose to physically run this cable.
You also need to explain what relay it is you want to control and what the "water pumping mechanism" is, how it is powered and how you propose to connect the ESP8266. A 3.3 V relay is going to be inconvenient and an ESP8266 cannot operate a relay directly, so you basically should not be transmitting a 3.3 V signal along your wire.
If you provide some sensible information here, we can certainly advise how to arrange it, but so far, you are getting nowhere, fast. 