I wired my Everydrop up using standard 18/6 sprinkler wire and it works just fine. My wire run is well over 100’.
14/2 house wire is huge for the current draw but if it’s free then I’m sure it will work fine. You might have to wire nut on a pigtail of 16 or 18ga wire to insert into the Rachio terminals. Good to know that the Rachio will only support one meter input to either the S1/S2 ports.