Buzz
Anti-siphon valves offer a perfect example of how building codes evolve. They also highlight how some code rules that may seem illogical can actually resolve significant issues. Today, most building codes mandate the installation of anti-siphon valves in multiple locations within a home, including all outdoor hose connections and, at times, in toilet fill valves.
Let's begin by defining a siphon. A siphon is any pipe, hose, or tube used to move liquid from a higher position to a lower one. To use a siphon, fill the pipe or hose with liquid and place one end at the higher location. Then, as the liquid starts draining at the lower end, a vacuum forms, which draws water from the higher end. Gravity and suction handle the rest, so no pump is needed! Siphons can be used to drain ponds, empty barrels, or even remove gasoline from a tank.
Here's the issue that anti-siphon valves resolve: Imagine you're using your garden hose to fill a 300-gallon aquarium in your upstairs bedroom. As you turn on the water, the hose fills. When the aquarium is full, the hose's submerged end is covered by water. If the water pressure drops—say, due to a power outage in a rural area with a private well, or in the city due to a fire hydrant being opened—what happens next is that the aquarium water will siphon back through the hose into your home's water system. The next time you turn on the kitchen faucet, you might be drinking aquarium water. Gross! This problem is even more severe if the hose is used to fill a pesticide tank. In lawn irrigation systems, if there's standing water in the yard, the siphon effect could pull harmful substances like fertilizer, weed killers, or even pet waste into the plumbing. Double gross!
The anti-siphon valve prevents all of these issues. Essentially, it's a one-way valve. It could be as simple as a spring-loaded flap that only permits water to flow in one direction.
An important point to consider is that many people overlook the anti-siphon valve. This may be because they're unaware of it, don't fully understand its purpose, feel that it's too costly, or simply don't like being "told what to do." In doing so, they put both their own health and their neighbors' health at risk, as the anti-siphon valve addresses a real problem. This is precisely why building codes and inspections are in place.
