drawing the water from the airlock.

if it has completely stopped fermenting, and what you're noticing is that the water seems to be going the wrong way, but not actually bubbling back into the vessel, then what you're probably seeing is a result of a drop in temperature.

As the air or co2 in your fermenter cools, it takes up less space and sucks at the airlock a little. If that's what it is, you don't need to worry.

perhaps there was a sharp drop in the barometric pressure? when the last big low pressure area swept across our region, we noticed some creepage up the air locks.

When you ferment, the temperature is elevated and the must is giving off CO2. When it stops, the temperature drops causing the volume to contract lowering the pressure. This can cause air to be drawn into the carboy. It is usually no a problem as the fermentation should stop slowly and the temperature should adjust slowly.

Now remember that the airlock is a low pressure lock. If there is a large swing in air pressure, the pressure in the carboy can only adjust by blowing out or drawing in. This could cause bubbling. Or if there is a temperature change the volumes in the carboy will expand and contract causing airlock movement. Usually the volume in the airlock itself should be sufficient to take care of these changes. The fluid should just swing from one side to the other but not pass bubbles. But if there is too little fluid in the airlock then bubbling will happen. If there is too much fluid the some airlock fluid may spill into the carboy. Not a good thing. If filled properly, an airlock should have enough volume to properly protect a properly filled 5 or 6 gallon carboy. You really do not want bubbles going into the airlock or certainly not much.

Now here is an interesting thing to note. The airlock should protect you if you have the carboy filled properly. It should be filled up to within 1 or

1.5 inches of the bottom of the bung. Some people recommend using inert gas to protect an improperly filled carboy. But any gas is much, much, much more effected by temperature and pressure changes than is liquid. So if you have several inches of head space, even if it is filled with inert gas, a few degrees of temperature change could easily cause a lot of air to pass through the airlock. After a few days of 3 or 4 degree temperature changes night to day or AC on/off could bring a lot of air into your carboy.

Ray