Tosefta for Zevachim 149:6

Waters of purification into which fell waters from a spring, or waters from a mikveh or fruit juices: If the majority are waters of purification, they impart impurity by carrying; [and] if the majority are fruit juices, they do not impart impurity by carrying. Half and half -- they impart impurity by carrying. In any of these cases, they are disqualified from sprinkling from them. Said Rebbi, according to the words of Rabbi Eliezer, a sprinkling in any amount is fit [to purify], and [even if the sprinkling is] half from fit [waters] and half from unfit, the sprinkling purifies in any amount.