A Clear Answer to a Common Question
If you’re wondering how often you should run water in an unused shower, the straightforward answer is this: you should aim to run water for a minute or two at least once every two to four weeks. While this simple rule of thumb works for most homes, the ideal frequency can actually depend on several factors, including your home’s climate, humidity, and the season. Neglecting this small task can, believe it or not, lead to some rather unpleasant consequences, from foul odors to unwelcome pests making their way into your home. This article will dive deep into why this simple act of maintenance is so crucial, help you determine the perfect schedule for your home, and provide a step-by-step guide on how to do it right.
The Unsung Hero in Your Bathroom: Understanding the P-Trap
To truly grasp why running water in a guest or unused shower is so important, we first need to talk about a crucial piece of plumbing hidden from view: the P-trap. You may not have ever seen it, but every drain in your home—from your sinks to your showers and floor drains—has one.
The P-trap is the U-shaped section of pipe located just beneath the drain opening. Its simple, clever design is meant to hold a small amount of water at all times. This plug of water acts as a physical barrier, or a seal, that effectively blocks noxious, and potentially harmful, sewer gases from rising up through your pipes and entering your living space.
Think of it as a silent, diligent gatekeeper for your home’s plumbing system. As long as that water barrier is in place, everything smelly and unpleasant from the sewer system stays where it belongs. However, when a shower goes unused for a long time, this water barrier is threatened by a slow, silent process: evaporation.
What Happens When the P-Trap Dries Out?
When the water in the P-trap evaporates completely, the seal is broken. This creates an open, unimpeded pathway from the main sewer line directly into your bathroom. Here’s what can happen next:
- Invasion of Sewer Gas: The most immediate and noticeable consequence is the smell. You might start to notice a persistent, foul odor reminiscent of rotten eggs or raw sewage. This is sewer gas, a complex mixture of gases including hydrogen sulfide, ammonia, and methane. Beyond being extremely unpleasant, prolonged exposure to high concentrations of these gases can potentially lead to headaches, dizziness, and other health concerns.
- An Open Invitation for Pests: A dry P-trap is like an open door for small pests that thrive in sewer systems. Drain flies, which breed in the organic sludge inside pipes, can easily fly up through a dry trap. More alarmingly, cockroaches and even small rodents can navigate the sewer lines and use a dry pipe as an entry point into your home.
- Potential Damage to Fixtures: While the primary concern is the P-trap, the internal components of your shower fixtures also benefit from periodic use. Rubber gaskets and seals within the shower valve can dry out, become brittle, and crack over time if they aren’t occasionally exposed to water. This can lead to slow leaks inside the wall when the shower is eventually used again.
Determining the Right Frequency: How Often to Run Your Unused Shower
That general guideline of “every 2 to 4 weeks” is a fantastic starting point. But for those who want to fine-tune their home maintenance, understanding the factors that influence the rate of evaporation will help you create a more precise schedule. Water in a shower P-trap in a humid Florida home during the summer might last for over a month, while the same P-trap in a dry, heated Arizona home in the winter might dry out in just over a week.
Let’s break down the key variables that can affect how often you should run the water.
Key Factors Influencing P-Trap Evaporation
| Factor | Impact on Evaporation Rate | Recommended Action |
|---|---|---|
| Climate & Humidity | Homes in dry, arid climates (like the American Southwest) or at high altitudes will experience much faster evaporation. Conversely, homes in humid, damp climates (like the Southeast) will have much slower evaporation. | In very dry climates, check weekly or run water every 1-2 weeks. In very humid climates, you can likely extend this to every 4-6 weeks. |
| Seasonality & Indoor Heating/Cooling | Winter is often the fastest time for evaporation, not because of the cold, but because home heating systems dry out the indoor air significantly. Aggressive air conditioning in the summer can also reduce indoor humidity and speed up the process. | Be more vigilant during the winter months when the heat is running. You may need to run water more frequently (e.g., every 2 weeks) in winter than in the milder spring or fall (e.g., every 4 weeks). |
| Bathroom Ventilation | A bathroom with a powerful exhaust fan, a nearby open window, or a location in a high-airflow part of the house will see faster evaporation due to increased air movement over the drain. | If the unused shower is in a well-ventilated bathroom, lean towards the shorter end of the frequency spectrum, around every 2 weeks. |
| Infrequent Use of Nearby Fixtures | While each fixture has its own trap, significant pressure changes in the drain-waste-vent system (like from a flushing toilet) can sometimes cause a tiny amount of water to be siphoned from a nearby trap. If the whole bathroom is completely unused, this is less of a factor. | This effect is generally minor, but it’s another reason not to let all fixtures in a single bathroom sit completely idle for too long. Stick to the 2-4 week rule. |
The Right Way to Run Water in an Unused Shower: A Simple Guide
So, you’ve figured out your schedule. Now, what’s the best way to actually perform this task? It’s incredibly simple, but a few small details can make it even more effective for your plumbing’s long-term health.
- Run Both Hot and Cold Water: Don’t just turn on the cold tap. It’s a good practice to run the hot water for 30 seconds to a minute first. The warm water can help dissolve any soap scum or incipient gunk starting to build up in the P-trap. Then, switch to cold water for another 30 seconds to a minute. This ensures the trap is left full of cool water, which evaporates slightly slower than warm water, and it exercises both the hot and cold sides of your shower valve cartridge, keeping its internal seals pliable.
- Aim for a 1-2 Minute Runtime: You don’t need to run the shower for five or ten minutes. The goal is simply to flush the old, stagnant water and completely refill the P-trap with fresh water. A total runtime of 1-2 minutes is more than sufficient to accomplish this without wasting a significant amount of water.
- Don’t Forget Other Drains: While you’re in maintenance mode, think about any other drains that see infrequent use. This is especially common with basement floor drains, laundry room utility sinks, or sinks in a guest bathroom that is rarely visited. Each of these has its own P-trap that needs to be kept full. Simply pour a pitcher of water down these drains on the same schedule.
Advanced Solutions for Long-Term Absences
What if you’re dealing with a shower that will be unused for much longer than a month? This is a common concern for vacation homes, cabins, or for those who travel for extended periods. In these cases, simply refilling the P-trap might not be enough, as it could easily evaporate before you return. Luckily, there are a couple of excellent “pro-level” solutions.
The Mineral Oil Trick
This is a fantastic, low-cost, and highly effective trick used by plumbers. After you’ve run the water to refill the P-trap, slowly pour about 2-3 tablespoons of household mineral oil down the drain.
- How it Works: Mineral oil is lighter than water and does not evaporate (or does so extremely slowly). It will float on top of the water in the P-trap, creating a thin, protective barrier. This barrier dramatically slows down the rate of evaporation, extending the life of your water seal from a few weeks to many months, or even longer.
- Why Mineral Oil? It’s important to use a stable, non-perishable oil. Mineral oil is ideal because it won’t go rancid like cooking oils (e.g., vegetable or olive oil), which can create foul odors of their own and coat your pipes in a sticky residue. RV antifreeze (the non-toxic kind) is another viable option.
Automatic Trap Primers
For a truly permanent, set-it-and-forget-it solution, especially in a property that is frequently vacant, you can have a plumber install an automatic trap primer. This is a special valve that is connected to a nearby, frequently used cold water line (like a toilet supply line). Every time that fixture is used, the primer valve releases a tiny, measured amount of water through a tube that runs to the unused drain, automatically keeping its P-trap full. This is a professional solution that completely eliminates the need for manual intervention.
Final Thoughts: A Small Task with Big Benefits
At the end of the day, understanding how often you should run water in an unused shower is about proactive home maintenance. It’s one of the easiest and quickest tasks you can perform, yet it protects you from some surprisingly significant problems. That minute or two you spend every few weeks ensures your home is shielded from unpleasant sewer gases, thwarts potential pest invasions, and helps keep your plumbing fixtures in good working order.
By considering your climate and home environment, you can tailor a perfect schedule. And for long-term absences, a little bit of mineral oil can provide invaluable peace of mind. So, add a recurring reminder to your calendar and make this simple chore a part of your routine. Your nose, your health, and your plumbing will thank you for it.