The fresh water tank isn't pressurized, so I wouldn't expect that a leak would become a steady stream. Unless, the check valve in the pump is leaking and the fresh tank is getting back-filled.
But it's a drain, either for the fresh tank or low point of the pressurized system. Some have valves - see if there's a cabinet or access panel above where it pokes out. Others are supposed to have screw on caps to seal them closed - your's may have fallen off - it looks like there's thread tape there, but no cap. I'm assuming the leak is coming out of the end of that blue hose, not leaking through a fitting. If a cap is missing, it's almost certainly a fresh tank drain - water would be gushing out if it were pressurized.