Hurricane Harvey Flood Marks: Removing 2017 Waterlines

It has been almost nine years since Harvey dropped 50 inches of rain on Katy in a single week, and we still get calls every spring from homeowners who have a thin brown line running across their brick or stucco at waist height. That line is where the floodwaters sat for days against the house before receding. Most of the homes on the west side of Katy and the flooded parts of the Barker Reservoir overflow zone saw some version of this, and even after repairs, repainting, and years of normal weathering, the waterline is still there on many homes.

Here is what the stain actually is, why it is so stubborn, and how to get it off for good.

What the Waterline Actually Is

When floodwater sits against a wall for days, a few things happen simultaneously. The water itself contains suspended mud, organic debris, oil from flooded cars, fertilizer and pesticide runoff, sewage overflow from compromised lines, and whatever else was dissolved into the flood current. All of those things sit at the water surface and get pushed against any vertical surface the water is touching.

As the water level slowly drops, the contaminants concentrate at the water surface and settle onto the wall in a horizontal band. The band is usually half an inch to three inches wide, depending on how long the flood sat at that level, and it is darker than the surrounding material because of the mixture of mud, iron, and organic matter that got deposited.

On brick, the waterline penetrates into the porous surface and bonds chemically with the clay in the brick. On stucco and EIFS, it soaks into the topcoat. On painted wood, it bonds with the paint film. In every case, it is not just sitting on the surface. A hose will not remove it. Even normal pressure washing often leaves a ghost of it behind.

Why It Took Years to Become Visible Again

A lot of homeowners tell us that right after Harvey, they cleaned the outside of their house and the waterline seemed to disappear. Then a few years later, it started showing back up. This is not your imagination.

What happens is that the initial post-flood cleaning removes the surface mud and debris, which is the most visible part of the waterline. But the deeper iron and organic staining stays in the substrate. Over the next several years, as the exterior weathers and the surface film of mildew and dust builds up, the older stain underneath becomes visible again because it is reacting differently to the new surface layer. The waterline essentially "bleeds through" any surface cleaning you do after the fact.

That is why a house can be cleaned every year and still show the Harvey waterline in 2026. The deep bond to the brick or stucco was never addressed, only the top layer.

How We Remove It Properly

Removing a 2017 waterline requires a two-stage chemical approach. A simple pressure wash will not do it. Here is our process:

Stage 1: Surface cleaning. Standard soft wash of the whole affected wall with a biodegradable cleaning solution. This removes any current-year mildew or algae that has built up on top of the old waterline and gets us down to the underlying stain.

Stage 2: Targeted stain removal. We apply a dedicated iron remover (oxalic acid based) and an organic stain remover (sodium percarbonate based) directly to the waterline band. Both products work at the same time: one breaks down the iron and mineral staining, the other breaks down the organic staining. We use a soft bristle brush to agitate the product into the substrate, which is essential for getting the chemistry into the pores.

Stage 3: Extended dwell. Harvey waterlines are old enough that a 5-minute dwell is not enough. We apply the chemistry, wait 15 to 20 minutes, and reapply if the product starts to dry out. The chemistry has to have enough time to work through the bonded stain layer.

Stage 4: Soft rinse. Low pressure (under 500 PSI) to flush the dissolved stain away without eroding the substrate. The goal is to carry the loosened stain away gently, not blast it.

Stage 5: Neutralize. After acid treatment, we apply a mild alkaline rinse to neutralize the brick or stucco pH. This prevents the stain from becoming "stickier" to new pollutants in the future.

On a typical Katy home with a visible Harvey waterline across the front elevation, this process takes 3 to 4 hours and runs about $400 to $700 depending on how much of the house is affected and how severe the staining is. On homes where the waterline went all the way around the house (worst-case scenarios from 2017), the job can be a full day and run $800 to $1,200.

The Harvey waterlines are finally at the point where the chemistry can address them in one visit. In 2018 and 2019 they were still too fresh for a simple cleaning. In 2026 they have weathered enough that a two-stage treatment actually restores the brick. — A note from one of our longer-serving technicians

Whole-House vs Waterline-Only

Some homeowners ask if we can just treat the waterline band without cleaning the rest of the house. The answer is yes, but we usually recommend doing a full house wash at the same time. Here is why.

If we treat only the stained band and leave the rest of the wall dirty, the removed waterline will look noticeably cleaner than the surrounding area. That "clean stripe" is almost as visible as the original waterline, just in the opposite direction. By doing the full house wash at the same time, everything ends up at the same brightness and the waterline just disappears into the overall clean finish.

The cost difference between waterline-only and full house plus waterline is usually only $150 to $250, and the result is dramatically better.

Will It Come Back?

Once the waterline is properly removed with the two-stage chemical process, it should not come back as a visible feature. The deep bonded stain is gone, and the brick or stucco is back to its normal pH. Future cleanings can be the standard soft wash process.

The one exception: if the flooded area has continued to have moisture problems (poor drainage, a leaky downspout, sprinkler overspray), the same spot can develop new staining from other causes. That new staining is usually much lighter and easier to remove, and it is not specifically a Harvey flood mark anymore.

One More Thing: The Garage Door

If your house had floodwater inside the garage, the inside of the garage door often has a corresponding waterline on the interior panels. This is harder to address because garage doors are usually painted aluminum or steel, not brick or stucco. For those, the fix is usually cleaning plus touch-up paint, not chemical stain removal. We can clean them but usually recommend a body shop or painter for the repaint.

If You Still Have a Waterline

Almost nine years is long enough. If the line is still visible on your Katy home, send us a photo with your free quote request and we will give you a specific price based on what we can see. Most waterlines can be removed in a single visit, and the house looks dramatically better as a result. Or call us at (281) 555-0147.