When you’re in the middle of a bathroom renovation and discover something unexpected, it can be confusing — especially if it doesn’t look familiar at all. One common example homeowners encounter is small glass tubes, about two inches long, sealed on both ends and filled with liquid, hidden under a vanity or behind a wall.
Finding objects like this can spark a lot of questions: What are they? Why were they there? Are they dangerous? The good news is that in most cases, these tubes aren’t harmful and can be explained once you understand what purpose they serve.
In this article, we’ll explore what these glass tubes likely are, why they were placed there in the first place, and what you should know when you come across them during a renovation.
What Are Those Glass Tubes?
Those small sealed glass tubes you found are most likely moisture indicators or humidity control tubes that were installed during construction or by a previous remodeler. They are often called:
- Humidity indicator tubes
- Moisture sight gauges
- Desiccant monitoring tubes
These tubes contain a special liquid or substance that reacts to moisture in the air. In some cases, the liquid itself changes color to show whether humidity inside a wall cavity is too high. In other cases, the tube may be part of an old mechanical system designed to help monitor moisture levels in enclosed spaces.
Why Were They Placed There?
There are a few common reasons these tubes might have been installed under a vanity or in a bathroom wall:
1. Monitoring Moisture During Construction
Bathrooms are high‑humidity environments. When a bathroom is newly built or remodeled, builders sometimes install moisture indicators to monitor how well the space dries out after plumbing and tiling work. Installing a tube in a hidden area lets professionals check for trapped moisture without tearing open a wall later.
2. Part of an Old Plumbing or HVAC Inspection System
In some older homes, moisture gauges were installed as part of:
- Early humidity control systems
- Inspection points behind vanities or cabinets
- Systems meant to track humidity before modern digital sensors existed
These systems helped contractors make decisions about ventilation and drying times.
3. Leftover From a Previous Remodel
If the house has been remodeled previously, the tubes might simply be leftover equipment that was never removed after completing the work. Sometimes contractors place temporary monitoring devices and forget to take them back out.
What Is the Liquid Inside?
The liquid inside these tubes is usually not dangerous. It’s typically:
- A color‑changing indicator liquid used to show humidity levels
- A non‑toxic solution that responds to moisture in the air
- Sometimes a desiccant indicator, which changes color as it absorbs water vapor
The exact composition varies depending on the manufacturer, but it is generally sealed inside the glass and not harmful unless broken.
Are These Tubes Dangerous?
In most cases, no.
These tubes are sealed and not pressurized. They are designed to contain the liquid safely. Unless the tube is broken open, the liquid shouldn’t pose a health risk.
However, if you accidentally break one:
- Avoid direct contact with the liquid
- Wash your skin if contact occurs
- Clean it up with a paper towel and discard it with normal trash
- You don’t need special disposal unless labeling indicates otherwise
If you’re in doubt, take a quick photo of the broken tube and consult a professional, but these indicator liquids are generally safe.
Should You Remove Them?
Yes — once you understand what they are, it’s usually fine to remove them. A few tips:
- Wear gloves when handling anything that has been behind walls or vanities
- Inspect the surrounding area for moisture damage or mold before closing things up
- Dispose of old tubes properly (most can go in regular trash unless marked hazardous)
Since these tubes are for monitoring and not part of the structural or plumbing system, removing them should not affect your remodel.
What to Do if You’re Unsure
If you find any object during a renovation and you’re uncertain what it is, consider these steps:
1. Take a Close Photo
A clear image of the object and its location helps if you need to ask a professional later.
2. Note Any Markings or Labels
Sometimes even tiny labels can provide clues about the manufacturer or purpose.
3. Ask a Contractor or Remodeler
If you’re working with a contractor or have one inspect your home, they can confirm what the object is and whether it needs to be kept or removed.
4. Avoid Guessing
It’s better to ask first than assume something is harmless — especially when dealing with electrical, plumbing, or structural elements.
Conclusion :
Finding small glass tubes filled with liquid under a bathroom vanity during a remodel can feel strange, but in most cases, there’s nothing to worry about. These tubes are often leftover moisture or humidity indicators used during construction or renovation to help professionals monitor conditions behind walls and cabinets. They’re usually sealed, non‑toxic, and safe to remove once you’re ready to finish the project.
Understanding what they are and why they were installed helps take the mystery out of unexpected finds like this. If they’re old and no longer needed, it’s usually fine to discard them and continue with your renovation work. Just be sure to handle them carefully, inspect the area for signs of moisture or damage, and consult a professional if you have any uncertainty.
Renovations often bring surprises, but with a little know‑how and patience, those surprises become part of the adventure of making your space better.
