What Are the Causes of Rust in a Toilet Tank

Rust in a toilet tank can be scary. It seems like it should be confined to bridges, ships, and other sites with corrosion. Your toilet tank is supposed to be rust-free. Many people become nervous when they find rust in their toilet tanks, and they don’t know what it means. Does that mean your toilet is broken? Not – unless the rust has eaten through the metal. There are some common reasons for rust stains in toilet tanks:

Water That Is High in Iron

The most common cause of rust in toilet tanks is water containing high iron levels. This can happen when you use water from a well or municipal system with a lot of iron. Iron is a metal that naturally occurs in the earth’s crust, and it’s what gives soil its reddish hue. Water that flows through iron-rich soil picks up iron particles and carries them along as it moves through the ground and into wells and municipal water systems.

The iron in your toilet tank may not be visible at first. However, over time, the iron will turn into rust, and if left unchecked, it’ll begin to damage your toilet’s inner workings.

You can prevent this by filtering out the excess iron before using your water for everyday tasks like flushing toilets or taking showers.

Very Acidic water

If your water has a very low pH, it can cause your toilet tank to rust. This is especially true if you have hard water, meaning that it contains high levels of minerals like iron and magnesium. When these minerals come in contact with acidic water, they can create rust.

In some cases, this may occur naturally over time as hot water passes through pipes that contain iron or copper. However, acidic water from the tap can also lead to corrosion in the tank.

If you suspect that your toilet tank is rusting due to acidic water, try adding a small amount of baking soda and vinegar to the tank. The baking soda should neutralize any acidity in the water, while the vinegar will help clean off any built-up residue inside the bowl.

toilet tank with rubber toilet seal
Image from The Lord Is My Helper Handyman Service

Problems With the Toilet Seal

The seal between the toilet tank and bowl is usually rubber or plastic. It keeps water from leaking out of the tank, but it can also develop leaks. Toilet seals are often the cause of rust in a toilet tank.

If you have a leaky toilet seal, you may notice that water is slowly leaking into your toilet bowl. This will cause rust stains around the base of your toilet bowl. The stains are caused by iron oxide, which is found naturally in water.

Hard Water

Water is the leading cause of rust in a toilet tank. If you live in an area with hard water, your toilet tank will most likely develop rust. Hard water contains minerals such as calcium and magnesium that can cause corrosion on metal surfaces.

The water supply to your home may be particularly corrosive if you live in certain areas where the water comes from wells fed by underground aquifers.

Toilet tank manufacturers recommend using water softeners or filters to reduce the amount of these minerals in your household’s water supply.

flush valve
Image from Luis Your Plumber LLC

Problems With Your Flush Valve

The flush valve is the part that flushes water into the bowl. It’s a device that opens and closes to let water into the bowl, so it’s not surprising that it can cause problems.

If you have a flush valve that doesn’t work correctly, this could cause rust in your toilet bowl and tank and make noises when flushing. The flush valve mechanism could also be rusted and corroded as well as causing problems with running water pressure and flow rate during flushes.

Other Causes of Rust

  • Rust can also form because of mineral deposits in your toilet tank. These deposits can come from sediment that settles at the bottom of your toilet bowl after flushing or from hard water deposits inside your toilet tank’s lid and bowl.
  • Corrosion caused by mineral deposits is usually minor and cosmetic only; however, it can affect how well your toilet works by slowing down flushing or clogging the drain line between the tank and bowl due to clogged holes through which water flows into the bowl when flushed
  • The water level in your toilet tank is too high. The water should be just above the flush valve, not up to the top of the tank. The higher it is, the more likely it will rust over time.
  • The other most common cause of rust is when someone uses too much bleach or another harsh chemical in their toilet tank. This can also damage the tank over time.
  • Another cause of rust in toilet tanks is aging metal parts exposed to moisture over time. The metal oxidizes and corrodes, causing rust stains on the inside of your toilet tank.

How to Prevent Rust in a Toilet Tank

We all know that water plus metal equals rust. However, it’s not a given that you will see rust on your toilet tank unless you do something to invite it. Here are some tips to prevent rust on your toilet:

Use a Siphon Jet Flush System: Rust is caused by the water evaporating from the tank and leaving behind minerals that then deposit on the tank’s surface as rust. The siphon jet flush system prevents this by ensuring that water remains in contact with the tank’s surface at all times.

cleaning a toilet tank

Clean and dry the inside of the tank regularly. Use a soft cloth or paper towel to wipe down the inside of the tank after each use. This prevents water from staying pooled in hard-to-reach areas, where it can go stagnant and cause rusting over time.

Use a non-abrasive cleaner and baking soda when needed. If cleaners leave behind any residue, scour it away with baking soda and warm water, then rinse with cold water after cleaning. Never use steel wool or other abrasives because they can scratch the inner surface of your tank and cause rusting even sooner than if you hadn’t cleaned at all!

Never leave bleach or harsh chemicals in the tank for extended periods! These chemicals can eat away at the porcelain of your toilet tank over time and lead to cracks that allow outside moisture into the interior space, leading to rust spots forming on your shiny white porcelain bowl.

How to Fix Rust in a Toilet Tank

Rust in a toilet tank is a common problem that can be easily fixed. Rust in toilet tanks is caused by water sitting in the tank for long periods. The water causes the metal to corrode and rust. This can lead to problems with your toilet flushing and leaking into your basement or garage if it’s not taken care of promptly.

toilet tank with rust
Image from 419 Remodel & Design

A toilet tank is one of the most used parts of your bathroom, but it’s also neglected. It’s also one of the most difficult to maintain, especially when rusting. While rust isn’t a health concern like mold or mildew, it can be unsightly and damaging to your home’s plumbing system.

Rust can form on the inside of a toilet tank when it becomes exposed to water that has been sitting for long periods. This water can contain minerals such as iron and copper that oxidize when exposed to air. The oxidation process produces rust, which will eventually cause your toilet tank to leak if left untreated.

The first step in fixing your toilet tank is knowing what type of metal it’s made from so you know how best to treat it:

Clean the tank out thoroughly: Clean out any rust deposits with an old toothbrush or sponge. Scrub away stubborn spots using steel wool or a wire brush, then wipe everything down with your vinegar solution and dry thoroughly with paper towels or rags (if using steel wool or wire brush).

WD-40 spray

Apply rust remover to the affected areas: Spray some WD-40 into all openings in the bottom of the tank, including overflow tube holes, drain holes, and water level sensor holes (if equipped). This will help prevent future corrosion problems inside these areas of your toilet tank when it’s refilled with fresh water after being cleaned out thoroughly with vinegar solution.

Scrub off any remaining rust with steel wool or sandpaper. If there is a lot of rust, you can use a wire brush attachment on your drill to remove it faster and more effectively than by hand.

Paint over the area with a coat of primer paint (optional). If you want to cover up the rust instead of eradicating it, paint over it with a coat of primer paint after you have scrubbed off as much as possible. Ensure that you get adequate coverage for this step—the better quality primer will be better at covering up any remaining rust spots than less expensive brands.


In the end, you can’t stop rust from coming back even after you remove it, but you can try one more thing. You can pour bleach and water into the toilet tank and wipe the inside and down below with bleach wipes. This will prevent rust from coming up again.

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