By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange County

Jeff Burbrink

LAGRANGE — I was once again reminded that I have to pay attention to details, or bad things can happen.

Like many rural landowners, I have frost-proof water hydrants on my property, which are used for anything from filling livestock and pet watering tanks, to watering gardens or lawns, to washing the car or filling spray tanks for pesticides. These hydrants are connected to a supply line that leads to your well.

In Indiana, the supply line is typically buried 40 or more inches below the soil surface to avoid freezing. The hydrant itself is a long pipe with an internal rod, the rod opens and shuts the valve that connects to the supply line.

The added feature that keeps the hydrant from bursting in cold weather is a drain hole built into the shut off valve. When the handle is moved to the water-off position, the rod shuts the valve, and the remaining water drains via gravity out of the pipe, typically into a gravel packed around the base of the hydrant. It is an ingenuous way to run water to remote parts of the property with little risk of freezing pipes.

There is one risk to this simple system: back siphoning. If there is a hose attached to the hydrant, and the hose end happens to be in the fluid in the tank, the flow of the water down through the drain hole can create a siphon, and suck the contents of the container back through the hydrant, and deposit them in the gravel at the base of the hydrant, 40 inches plus below ground. Once down there in the soil, there is no way to get that fluid back under control.

An illustration of the below ground layout of a typical frost free hydrant used in Indiana. Illustration from the University of Nebraska.

In my case, I left the end of the hose in my dog’s watering bucket. When I shut off the hydrant, I walked away to do some other chores, and when returned 5 minutes later, the bucket was empty. Now, I am not too concerned about the dog’s water contaminating the soil and groundwater around the hydrant, of course; but what if the hose had been in my 50-gallon spray tank that I use for fertilizer and herbicide applications? That would have been a mess.

There is a simple remedy to this back siphon issue. Leave a gap between the end of the hose and the fluids in the tank. When gravity pulls the water back down the pipe, there will be no way to draw fluid from the tank. The other method, even more reliable, would be to disconnect the hose, but many of us do not do that out of convenience.

In food preparation businesses, they typically are required to have a minimum of a 6-inch air gap to prevent back siphoning from drains and such, and that certainly would work with hydrants servicing rural needs.

There are also specially designed hydrants that are sanitary as well as frost free. These specialty devices allow water to drain from the pipe below the frostline, while not allowing groundwater to reenter the pipe through the drain hole. These may be ideally suited for those who grow produce.