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. Flood staining may call for an iron remover, an organic stain remover, or both, depending on the material and stain type. Agitation, dwell time, and product compatibility should be reviewed before treatment.

Stage 3: Extended dwell. Older Harvey waterlines may need longer chemistry contact than routine staining. Dwell time should be adjusted for surface material, stain severity, weather, runoff, and product behavior.

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, neutralization may be needed for brick or stucco. Product guidance and surface condition should determine the rinse and follow-up method.

For a Katy home with a visible Harvey waterline, quote review depends on how many elevations are affected, the substrate, stain severity, access, landscaping, and whether the staining wraps around the house. Heavier or all-around staining can require more treatment time than a small front-elevation band.

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 flood-cleanup planning note

Whole-House vs Waterline-Only

Some homeowners ask whether to treat only the waterline band or review the full house wash at the same time. The answer depends on staining severity, surface type, access, and whether surrounding areas also show buildup.

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 quote should separate waterline-only treatment from any full-house wash so you can compare the scope clearly before scheduling.

Will It Come Back?

If the waterline responds to treatment, future maintenance may be closer to a standard soft wash. Results depend on substrate condition, stain depth, moisture history, and whether the source of staining is still active.

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, and repainting questions may need a painter or body shop.

If You Still Have a Waterline

If the line is still visible on your Katy home, send photos with your quote request so the substrate, stain severity, access, and treatment options can be reviewed.