Q. Water feature has chlorine residue buildup causing a white stain on natural rock waterfall. How can I remove the chlorine residue from the rock?
A. What you are seeing is likely mineral deposits. Chlorinated water doesn’t cause the deposits, but it keeps the water oxidizing, which can sometimes make the deposits appear more noticeable or accelerate crystallization in areas like waterfalls, fountains, or spa surfaces. Over time, repeated evaporation of chlorinated water concentrates these minerals, leaving that familiar white film on rocks, tiles, and metal surfaces.
There's a difference between a stain and a deposit, and the reason this is relevant is that the cleaning approach you will take will be different. A stain is when a pigment, chemical, or dye penetrates the pores of the stone. Stains often require a poultice or chemical treatment. A deposit, on the other hand, sits on the surface of the stone and is usually mineral-based, like lime scale, calcium carbonate, or salt residue from chlorinated water. Deposits don’t penetrate the stone—they just form a crust. They’re typically removed with mechanical cleaning, brushing, or mild chemical descalers, depending on whether the stone is acid-sensitive.
For your waterfall, the white marks are likely deposits, not stains, which means they can usually be lifted without risking the color or texture of the rock itself. How you remove it depends on the type of stone, because the wrong cleaner can permanently etch certain types of stone. Consulting with a stone restoration contractor would be advisable. To find a vetted PRO in your area, visit www.surfacecarepros.com and click on Find a PRO.
Here’s the safe, homeowner-friendly way to approach it: First, figure out whether the stone is calcium-based, like limestone, travertine, marble, tufa, some sandstones, or silica-based, like granite, basalt, slate, quartzite. Calcium-based stones are sensitive to acids, so you can’t use anything acidic to remove mineral deposits without risking damage. Silica-based stones can usually handle mild acidic cleaners.
If you don’t know the stone type, start gently. Try a non-acidic mineral deposit remover or even a strong alkaline cleaner meant for stone and masonry. These products loosen scale without etching. Follow the manufacturer’s safety precautions.Scrub lightly with a nylon brush and rinse very thoroughly. Sometimes a few passes are needed.
If the stone is definitely granite, basalt, or other acid-resistant rock, you can use a mild acidic stone-safe descaler to dissolve the chalky film, again brushing lightly and rinsing well.
If the residue has been building up for years, or the stone is delicate or very textured, you should probably entrust the work to a stone restoration PRO. They can remove the buildup with controlled cleaning that won't cause damage to your waterfall.
ABOUT THE AUTHOR Fred Hueston is the Chief Technical Director at SurfaceCarePROS.com and Director at StoneForensics.com. He is also the author of Stone and Tile Restoration: The Manual, a comprehensive online manual for stone and tile restoration contractors. [Learn more about Fred.]
Article ID: 822
Created: November 16, 2025
Last Updated: December 4, 2025
Author: Fred Hueston
Online URL: https://surfacecarepros.com/kb/article/how-to-remove-chlorine-residue-from-a-natural-rock-waterfall-822.html