That rumbling sound? Probably sediment. Here's what's actually going on inside your tank.
If your water heater is making popping or rumbling noises, running out of hot water faster than usual, or producing cloudy water — sediment buildup is likely the cause.
The good news: Sediment is normal. Every tank water heater develops it over time. It's not a sign that something is broken or that you did anything wrong.
The reality: Left unchecked, sediment can reduce efficiency, shorten your heater's lifespan, and eventually cause real problems. Understanding what's happening helps you make better decisions.
Sediment is mineral buildup — mostly calcium and magnesium — that settles at the bottom of your water heater tank. These minerals are naturally present in your water supply, especially if you have hard water.
When water is heated, minerals separate out and sink. Over months and years, they accumulate into a layer of sediment. In some cases, this layer can become several inches thick.
Three main factors determine how fast sediment accumulates:
Curious how much sediment might be affecting your tank? TankSediment.com has a calculator that estimates buildup based on your water heater's age and local water hardness.
Sediment doesn't announce itself until it's significant. Here's what to watch for:
This is the classic sign. Water trapped under the sediment layer boils and creates steam bubbles. When those bubbles escape through the sediment, you hear rumbling, popping, or crackling sounds.
It sounds alarming, but it's not immediately dangerous. It is, however, a clear signal that sediment has built up significantly.
Sediment takes up space in the tank. A thick layer means less room for actual hot water. If you're running out of hot water faster than you used to, sediment may be the reason.
Sediment acts as insulation between the burner (or heating element) and the water. Your heater has to work harder and longer to heat the same amount of water. This also increases energy bills.
Sometimes sediment gets stirred up and comes out of your faucets. Cloudy, sandy, or rust-colored hot water can indicate significant buildup — or other issues worth investigating.
It depends on how much has accumulated and how long it's been there.
Most people don't think about sediment until they hear the noise or notice a problem. That's normal — but it's also why understanding your options matters.
The standard solution is flushing the tank — draining water to remove sediment. Some homeowners do this themselves; others call a professional.
Before deciding, it helps to understand:
Popping, rumbling, knocking — what each sound means and when to worry.
Separate "annoying" from "urgent" — know when it actually matters.
What's involved, what can go wrong, and where to draw the line.
Signs that professional help is the smart choice.
Yes, tankless heaters need flushing too — here's why and how often.
The hidden part that keeps your tank from rusting — and when to replace it.