irrigating with field drain (conventional ag)

The fields above our veg plot are drained underground, the water feeds a fountain in the farm courtyard below. This used to be drinking water but is potentially contaminated by field runoff. I am now planning to divert some of this drain water to irrigate the garden, but am unsure if it is "safe"
- to use for drip irrigation
- to use for overhead sprinkler systems
- to use for underground irrigation (running through weeping pipe)
The catchment area is fields, orchard and vineyard in conventional ag, not all owned by the farm, but there is no sign at the moment of overfertilisation (no copper deposits for ex.) though when the fields are manured the water smells a bit I'm told. Is it necessary to test the water?

I'd be more concerned with herbicides and pesticides than fertilizers, especially since it's from various feilds,since one feikds weeds us another feilds crop.

Susan, if there is high-nitrate fertilizer coming from a large commercial farming operation that is getting into the water, you can test the water for that.  It can be filtered out pretty well with a charcoal filter that can be connected in the water line before it goes into a tank.  If there's no tank, then just an inline water filter before the faucets.   Nitrates and nitrites are what are also in high levels in cured meats like bologna, salami and bacon, and those aren't turning out to be good things.

If it's a dairy farm and they are giving the cows hormones and antibiotics, or there's a chance of e. coli getting into the water from dense piles of manure, then it's best to use the water on landscape plants only, not even fruit trees.  You'd probably need a lab to determine levels of those substances.

What's the source of the contamination you are suspecting?  Or maybe the question is, how big of an operation is it, and how far away is it?  Are you sure you are "downstream" from it?

pathogenic bacteria would be the biggest concern it sounds like to me.  (try some fresh bleach drops in a sample, if there are things that will form chlorates they will precipitate out)