Rainy Season and High Water Tables: Why Florida Drain Fields Struggle in Summer

Florida gets most of its rain in summer, and the ground under a drain field can fill with water. A drain field only treats wastewater well in soil that is not saturated, so when the water table rises it accepts less, drains slowly, and can back up into the house or surface in the yard. During a wet spell, Florida DOH and the EPA advise using less water and not pumping the tank while the ground is saturated.

This guide explains why summer is hard on drain fields, what Florida's 24-inch water table rule has to do with it, which signs to watch, and when a problem is more than a wet week. If you are dealing with a hurricane or flood, read your septic system after a hurricane or flood instead.

Florida's wet season

The Southwest Florida Water Management District says Florida receives most of its rainfall in 4 months, June to September, averaging 6 to 9 inches of rain a month. The dry season, October through May, averages only 2 to 3 inches a month.

The National Weather Service office in Tampa Bay dates the rainy season from May 25 to October 10 for most of West Central Florida (May 15 to October 15 for Southwest Florida). It describes 3 phases: late May through June, when severe storms are most likely; July through early September, when rainfall peaks; and mid-September through early October, when the season winds down. The weather service notes that the start can be abrupt or take weeks, so the beginning is usually a transition period rather than a single date.

Why a wet summer is hard on a drain field

A septic tank holds wastewater so solids settle out, then sends the liquid to the drain field. The EPA describes a drain field as a "shallow, covered, excavation made in unsaturated soil." The soil "accepts, treats, and disperses wastewater" as it moves down. The drawing shows the path.

How a conventional septic system works

1Wastewater from toilets, showers, sinks and laundry flows out of the house through one main drain pipe to the septic tank.
2In the tank, solids settle to the bottom as sludge, and grease and oils float to the top as scum. Compartments and a T-shaped outlet (often called baffles) keep both inside the tank.
3The liquid in the middle (effluent) flows out of the tank, in many systems through an effluent filter that holds back small solids.
4In many systems, a distribution box splits the effluent evenly between the drain field lines.
5The drain field is a shallow, covered area of unsaturated soil that accepts, treats and disperses the effluent. If it is overloaded or flooded, sewage can surface in the yard or back up into toilets and sinks.

A conventional septic system. Simplified illustration, not to scale; aerobic and mound systems add parts not shown here. Based on U.S. EPA, How Your Septic System Works.

When the soil around the field is already full of rainwater, there is less room for wastewater to go. UF/IFAS Extension puts it simply: "Saturated soil reduces the drainfield's ability to accept and treat wastewater." The EPA says a drain field overloaded with liquid can flood, sending sewage to the ground surface or backing it up into toilets and sinks. It also lists "high ground water tables" among the site conditions that can cause drain fields to fail.

The 24-inch rule and the "wettest season"

Florida's septic rule is written around the wet season. For a new system, Rule 62-6.006, F.A.C., requires the water table "at the wettest season of the year" to be at least 24 inches below the bottom of the drain field. Systems may not go where the natural wet-season water table is at or above the ground surface, unless enough permitted fill is brought in to build a proper system on the raised lot.

The rule tells evaluators how to estimate that wet-season level: soil survey maps, soil color and mottling, impermeable soil layers, on-site vegetation, and an on-site evaluation that considers the season, "historic weather patterns, and recent rainfall events." The same rule says the drain field site must not be subject to saturation from roof drains, driveways, roads or artificial drainage.

Repairs follow Rule 62-6.015. For repairs it allows less separation than 24 inches when the full amount cannot be met, but it also says nothing in it allows "a drainfield to remain in the wet season water table." Where a nitrogen-reducing system is required and a repair is allowed with less than 24 inches, DEP says the nitrogen-reducing unit itself must remove at least 65% of nitrogen before the drain field. Our nitrogen-reducing septic guide explains those areas.

What this means for you: a system permitted under these rules was sited with the wet season in mind. Older systems built with less separation, and low lots in very wet years, may still see the water table come close to the field. For background on Florida soils and system types, see how a septic system works in Florida.

Signs your drain field is struggling

The EPA lists these warning signs of a failing system. In summer, several of them can show up after heavy rain:

Water and sewage backing up into the home's plumbing
Tubs, showers and sinks draining very slowly
Gurgling sounds in the plumbing
Standing water or damp spots near or over the tank or drain field
Sewage odors around the tank or drain field

Wet ground alone does not prove a failure in the rainy season. The EPA says soft, wet or spongy soil around the drain field is a good sign of failure "especially when there have been no significant rainfall events." So tell the septic company how much rain you have had. If the signs come and go with the weather, mention that too. If you see or smell sewage on the ground, Florida DOH says everyone, pets included, should avoid the area. Keep people and pets away and call a septic company. Our list of 7 signs a septic tank is full or failing covers each sign in more detail.

What to do during a wet spell

Use less water

The Florida Department of Health advises homeowners on septic with slow or sluggish plumbing to "minimize water use as much as possible." The EPA says that when the water table is high, using the system less is the only way to prevent sewage from backing up. Practical ways to do that, from the EPA's septic care guide:

Spread laundry over the week instead of doing it all in one day.
Fix leaks. The EPA says a single leaky or running toilet can add as much as 200 gallons of water a day.
Run only full loads of laundry, or pick the right load size if your washer lets you.

After storms, Florida DOH suggests considering a rented portable waste receptacle if using your plumbing creates a sanitary problem. Florida's septic rule normally limits portable toilets at homes unless DEP has issued an emergency order, so ask your county health department first.

Do not pump the tank while the ground is saturated

It is tempting to call for a pump-out, but the agencies agree it is the wrong move while the soil is soaked. Florida DOH says not to have the tank pumped, because "exceptionally high-water tables" can make the surrounding ground cave into a tank that was pumped dry. The EPA says not to pump during flooded or saturated drain field conditions: at best it is a temporary fix, and the tank can try to float out of the ground. UF/IFAS says to wait until the soil is no longer saturated. Pumping removes what is in the tank, but it does nothing about the water in the drain field soil.

Keep extra water off the drain field

Gutters and downspouts: the EPA says to keep roof drains, sump pumps and other rainwater drainage away from the drain field, because "excess water slows down or stops the wastewater treatment process."
No driving or parking: the EPA says not to park or drive on the drain field. UF/IFAS adds keeping heavy equipment, dumpsters and building materials off the tank and field, and the EPA warns against compacting the soil over the field, especially while it is saturated.

Systems with a pump or an aerobic unit

Summer storms also knock out power. UF/IFAS notes that conventional gravity systems do not rely on electricity, but mound systems, advanced treatment units and other systems with pumps can be affected by an outage, while wastewater keeps collecting in the tank. If your system has a pump or an aerobic treatment unit, cut water use until the power is back, and call your maintenance company if an alarm goes off.

When to call a septic company

Sewage is backing up into the house. Use as little water as possible and avoid contact with the sewage, which the EPA says may contain harmful germs. Our guide to sewage backing up into the house covers the next steps.
Sewage or smelly water is on the ground surface. Florida DOH says everyone, pets included, should avoid areas where sewage has overflowed. Then call.
The signs continue after the rain stops and the ground dries out. That may point to a problem the weather does not explain. The CDC says that if you suspect damage, get the system professionally inspected and serviced.
A pump or ATU alarm is sounding.

A routine inspection runs about $100–$450. Ask the company to check the tank's levels and the outlet, and to look at the drain field, once conditions allow. For pumping prices and other jobs, see the Florida septic cost guide.

If your drain field struggles every summer

A field that floods every wet season may need more than patience. Repairing or replacing a drain field usually needs a permit from the county health department (Florida DEP in Marion County). Published ranges put drain field repair at about $1,000–$5,000 and full replacement at about $3,000–$15,000. The EPA notes mound systems are an option where groundwater is high, so on wet sites the fix may be a raised mound system; national cost guides put mound systems at about $10,000–$50,000. Our repair and drain field cost guide explains the options, and you can find drain field repair companies in the directory.

The dry season is a good time to plan. The EPA says skipping routine maintenance can let solids migrate from the tank into the drain field and clog it. The EPA recommends an inspection at least every 3 years, and our pumping interval calculator estimates how often your tank needs pumping.

Frequently asked questions

Should I pump my septic tank after heavy rain?

Not while the ground is still saturated. Florida DOH, the EPA and UF/IFAS all advise waiting, because a tank pumped in waterlogged ground can be damaged and pumping does not dry out the drain field.

Is a soggy yard after a storm a sign my drain field failed?

Not by itself. The EPA treats wet, spongy soil over the drain field as a warning sign mainly when there has been no significant rain. If the soggy spot stays after the rest of the yard dries, or it smells of sewage, have the system checked.

Why does my toilet gurgle only in summer?

Gurgling is one of the EPA's warning signs. UF/IFAS says saturated soil reduces how much wastewater a drain field can accept, but only an inspection can tell you the cause. Use less water in the meantime.

Does Florida require any distance between a drain field and the water table?

Yes. For new systems, Rule 62-6.006 requires the wet-season water table to be at least 24 inches below the bottom of the drain field. Repairs follow separate standards in Rule 62-6.015.

Do I need a permit to fix a flooded drain field?

Usually, yes. Florida law requires a permit to repair a septic system. Florida's septic rule does not count pumping alone, where the drain field is not disturbed, as a repair (Rule 62-6.002), so it does not need a repair permit. Local rules can differ, so ask your county permit office.