My hot water heater is under the house, in a crawl space, and it has a hose connected to it that leads to the outside of the structure. It is a small 1/2 inch hose, or so, and extends about 6" outside of the house. It just sticks outside the stucco and allows water to drip out. I am not sure what it is for, but recently it started dripping. It is releasing water from the hot water heater in a drip. The water is warm. Does anyone know what this means? I put a bucket outside and it filled up a 5 gallon bucket in 24 hours. I am going to have a plumber come, but I am just curious if anyone can help me understand what the issue could be?

thanks,
gc