There was a 20 year study conducted by a professor at the university of Georgia on Water Moccasins. They get a bad wrap for being too agressive. Most of the time they will leave the area when you are there. Their bite is more serious than the copperhead. A copperhead's best defence is to bite first and asks questions later. They are by nature a bit on the bold side so keeping your grass cut down doesn't deter a copperhead like a rattler.
A water mocassin bite can be deadly, no question about it.
A true story that occurred some years back on my shift when I was working 911:
One spring (1997, I think) we had had been having heavy rains/thunderstorms in the area. A man had been working helping to try to salvage some of the stock from a flooded store and was bit on the leg by a water mocassin. Trouble is, he didn't know it at the time, figuring he'd just snagged himself on something, and continued working. He worked for a couple of hours, then drove home. Shortly after arriving home, he began having complications which he reported to us. At the back of my mind was snakebite, but I couldn't say for sure as I wasn't there. So we paged the call out as a possible anaphylactic reaction, and medics and ambulance arrived promptly.
The ambulance was almost unusually quick in leaving with the patient, who had requested transport to a hospital in Birmingham, AL, about 30 miles away. While enroute the man coded, having gone into respiratory arrest, and we paged another rescue for mutual aid with the ambulance. The second set of medics (from another department) were very quick in responding and one of the medics stayed with the patient on board the ambulance all the way to the hospital.
Obviously it was some time before we heard the specifics, but we learned from the last medic who responded that the man was very lucky to be alive. I don't think he was dramatizing when he said that if he'd been thirty seconds later, the patient would have been going to the funeral home instead of the hospital.
So, yeah, I agree that water moc bites are pretty bad!