Rotten-egg smell in the hot water: the Jacksonville anode fix

The most Jacksonville plumbing call there is goes like this: the hot water started smelling like rotten eggs a few weeks ago, the cold water is fine, and somebody on the internet said the water heater is going bad. Usually it is not. The smell is hydrogen sulfide, and when it is in the hot water only it is usually being made inside the tank; on the First Coast that is a known property of the water and the heater rather than a sign of failure. JEA’s own guidance lists other sources too (a softener, a drain trap, the supply), which is why the first step is working out where and when the smell appears. Here is what is going on and what a plumbing contractor does about it.

Where the sulfur comes from

JEA’s water comes entirely from the Floridan aquifer, from wells about a thousand feet deep. Water that has sat in limestone that long picks up dissolved hydrogen sulfide, which is the rotten-egg gas. JEA’s treatment plants aerate the water to drive most of it off, and two of them use ozone as well, so by the time it reaches the tap the smell is gone or nearly gone. But the water still carries sulfate and a small population of sulfur-reducing bacteria, both harmless at the tap, and both of which matter once the water goes into a tank.

Inside a water heater, these meet: warm water that sits for hours, sulfate, and a magnesium anode rod. The anode is a sacrificial metal bar screwed into the top of the tank; it corrodes so the steel tank does not. When it corrodes it gives off hydrogen, and the sulfur bacteria use that hydrogen to turn sulfate into hydrogen sulfide. That is why the smell is in the hot water only, why it gets worse after a vacation or in a guest bathroom that is rarely used, and why it comes back a few weeks after a tank is drained. JEA’s own water quality material describes the same mechanism.

Hot only, or everywhere

Before anyone touches the heater, do the test that separates the two causes. Run cold water at a tap near the heater for a minute and smell it, then run hot.

• Hot smells, cold does not: the tank. This is the anode situation, and the rest of this guide applies.
• Both smell: the heater is not the source; look at the supply, a softener, or the house plumbing. On JEA water this is unusual; on a private well in Middleburg, Yulee or the county parts of St. Johns it is common. The contractor traces the source before recommending treatment (on a well, often an aeration or oxidizing filter), and the water heater is innocent.
• One fixture only, hot or cold: a drain, not the water. A dry trap or a biofilm in a sink overflow smells the same; run water and clean the overflow before calling anyone.

What the contractor does

When the heater is the source, the standard fix is to replace the magnesium anode with one the bacteria cannot use so easily, and to drain and disinfect the tank.

• Aluminum-zinc anode. A rod of aluminum with a small amount of zinc; the zinc suppresses the sulfide reaction and the aluminum still protects the tank. This is the common swap and the least expensive one.
• Powered anode. A titanium rod fed by a small plug-in power supply; it protects the tank electrically and produces no hydrogen at all. More to buy, nothing to consume, and the usual choice where an aluminum-zinc rod did not fully clear the smell or where the water is at the hard end of JEA’s table, on the Southside, in St. Johns or at Nocatee.
• Flush and disinfect. The tank is drained and rinsed to clear sediment, and often treated with a chlorine or peroxide solution for an hour to kill the bacteria already living in it, then refilled. Without this step the smell can persist for weeks after the new anode goes in.
• Sediment. A tank on 17 to 22 grains of hardness collects scale fast. The flush that goes with the anode swap also takes out the sediment that makes a heater rumble and shortens element life. Ask for it to be done together.

Getting the old anode out is the hard part: it is usually seized in the tank after years of use, and the hex head is under the top cover, sometimes under a low ceiling or in a closet where there is no room to lift the rod out. A flexible (segmented) anode solves the clearance problem; an impact wrench solves the seized one. This is the reason it is a contractor’s job in most Jacksonville houses rather than a Saturday project.

When the answer is a new heater

An anode swap on a heater that is twelve years old and rumbling is money spent on a tank that is close to its end anyway. Replacement is the answer when the contractor confirms the tank itself is leaking (water at the base can also be a fitting, the T&P valve, the drain valve, or condensation, all of which are repairs), or when the diagnosis weighs the tank’s condition, its age and the cost of the repair and comes out against repairing it; a rust-colored tint that persists after a flush, or a history of element and thermostat repairs on this water, is part of that picture rather than a verdict on its own. A replacement is a permitted job in Jacksonville, even like-for-like; the contractor pulls it through JaxEPICS in their own license. If you are replacing anyway, a heat pump water heater on a JEA electric account has a rebate, applied for within 90 days of installation, with the program year closing October 10, 2026; Clay Electric members have an Energy Smart bill credit. The amounts are on the utilities’ pages.

What to say when you call

Whether the smell is in hot water only or everywhere; the fuel and size of the heater and its age if the label shows it; where it sits (garage, closet, attic) and how much room there is above it; and whether the water has been off for a stretch recently. That is enough for a plumbing contractor to bring the right anode and plan the flush. The water heater page covers replacement, permits and the rebates in more detail.