The spring is on my property. The hill above it is not. Will the herbicide get in my spring water? Who knows? Very expensive to test and timing is important too, like after a heavy rain. Does the helicopter spraying near my house,orchard and vegetable garden hurt it? I don't know. The not knowing is stressful.  Thanks, 4%,I didn't know that. How far up the hill  would they go before they could spray?