I would say in general yes Water would affect Sponsored Magic just like normal because, as Melendwyr said, it's an objective Cleansing/Grounding force like Fire or the Sunrise. That being said, there are ways around it. It needs to be a fairly stead stream of actual running water. Harry has been able to do tracking spells in modest rain, it hinders but does not completely prevent the spell, just like doing one over the lake is possible but harder. Water magic could get you around it if you are thematically using actual water manipulation (not sure Carlos' Entropy Magic would give him the same insight). Strong enough Earth Magic might be able to withstand it; Ley Lines are unhindered by bodies of water, so it would go to the old Mountain vs River/Ocean theme. If the Earth magic could be channeled deep enough you could claim it's unaffected by the grounding properties of Water. Exotic enough sources of Power, especially any that grant resistance/immunity to magic, might get around it. Something like Outsiders, or a magic resistant curse like the Loup Garou, or Soulfire (since its supposed to have more metaphysical Mass, etc).