I once drank water from a natural spring in Kolomenskoye Park in the middle of Moscow. Tasted great with no ill effects. Don't know if it's safe for chronic consumption though.
95% it is safe. If it wasn't, it'd be marked as such. The spring doesn't need much space. Rain drops, gets filtered by sand and soil, comes out from a spring down bellow. A park of few hundred square meters is more than enough to be a safe filter.
Source: drink frequently from springs in/around towns.
Source: drink frequently from springs in/around towns.