It depends on several factors.
The condensed version is that every kind of supernatural ability the user has that isn't based on the element provides interfeerence.
Starting from an ordinary human wielding Aqua as "0":
A user with only water based abilities - 2
A user with mixed water and other type abilities - 1
A user with no abilities - 0
A user with only other type abilities - -1
A user with fire based abilities - -2
At -2, the sword begins rebelling against the wielder. Someone with fire based powers could technically wield Aqua, but the sword's magic would fight them every step, and they'd probably become crippled.
The condensed version is that every kind of supernatural ability the user has that isn't based on the element provides interfeerence.
Starting from an ordinary human wielding Aqua as "0":
A user with only water based abilities - 2
A user with mixed water and other type abilities - 1
A user with no abilities - 0
A user with only other type abilities - -1
A user with fire based abilities - -2
At -2, the sword begins rebelling against the wielder. Someone with fire based powers could technically wield Aqua, but the sword's magic would fight them every step, and they'd probably become crippled.