Sayyiduna Ibn Abbas (may Allah be pleased with them both) was asked about eight men who bathe in one pool, one of whom is junub (in a state of major ritual impurity). He (may Allah be pleased with him) said: "Water is pure; nothing makes it impure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1138