A shallow water table can limit basements, septic drain fields and lawns: USDA counts depth to a water table in its ratings for all three[1][2]. Enter an address or ZIP code to see how close to the surface USDA’s soil survey says the water table comes during the year.
US addresses only: street address, city and state, or ZIP.
The water table in USDA’s soil survey is a saturated zone in the soil that lasts a month or more[3]. For each map unit USDA reports its shallowest depth at any time of year and, separately, in April through June[4]. A shallow one limits basements, septic fields and lawns[1][2].
How to read the gauge
The top of the gauge is the ground surface. Each line marks a depth USDA reports, in inches and centimeters, and the blue below it is the saturated zone. “Not reported by USDA” means USDA has no value for this soil; we never estimate one.
How USDA estimates the water table
NRCS bases its estimate of the water table’s top mainly on observations at selected sites and on evidence of a saturated zone: grayish colors in the soil, called redoximorphic features. A saturated zone that lasts less than a month doesn’t count as a water table[3]. The soil survey stores a low, a high and a representative depth, and NRCS’s own water table maps use the representative one[3].
Grayish colors in a soil pit are evidence of a saturated zone; NRCS uses them to estimate how high the water table comes[3].
USDA drainage classes
Drainage class describes the soil’s natural drainage, the frequency and duration of its wet periods[4]. USDA’s seven classes, from driest to wettest[5]:
Class
What it means
Excessively drained
Water drains away very rapidly.
Somewhat excessively drained
Water drains away rapidly.
Well drained
Water drains readily but not too fast.
Moderately well drained
Water drains somewhat slowly at times of the year.
Somewhat poorly drained
Stays wet near the surface for significant periods.
Poorly drained
Wet at or near the surface for long periods.
Very poorly drained
Water sits at or near the surface most of the growing season.
Flooding frequency
USDA’s flooding classes estimate how often a soil floods, as a chance in any year[6]:
Class
Chance of flooding
None
No reasonable possibility of flooding: about 1 chance in 500 in any year
Very rare
Less than a 1% chance in any year
Rare
A 1 to 5% chance in any year
Occasional
More than 5 up to 50% in any year
Frequent
More than 50% in any year
Very frequent
More than 50% in all months of any year
These are a soil-survey estimate, not a FEMA flood zone. Lenders use FEMA’s flood maps to decide whether flood insurance is required, and the maps are free at FEMA’s Flood Map Service Center[7]. Soils on floodplains are often alluvial soil, built from sediment that streams and rivers drop when they flood[8].
6 in (15 cm) is the shallowest seasonal water table USDA reports for Blichton sand in Alachua County, Florida[9].
Worked example
Blichton sand in Alachua County, Florida: USDA reports the water table as shallow as 6 in (15 cm) at any time of year, and the same in April–June. The soil is poorly drained, and its flooding class is ‘None’[9].
Blichton sand’s seasonal water table, 6 in (15 cm) below the surface, from USDA’s soil survey (SSURGO)[9].
We read USDA’s map-unit values for the shallowest water table, at any time of year and in April–June[9][4], the drainage class of the main soil and the dominant flooding class[9]. Missing values show as “Not reported by USDA”. Depths are converted at 2.54 cm per inch[10].
Frequently asked questions
What is a seasonal high water table?
The shallowest depth a saturated zone in the soil reaches during the year. NRCS counts a saturated zone as a water table only if it lasts a month or more[3].
Is this the same as the depth of my well?
No. It is a saturated zone within the soil near the surface, estimated from soil colors and site observations[3]; it says nothing about the aquifer a well draws from.
What do grayish soil colors mean?
They are redoximorphic features, evidence of a saturated zone, and NRCS uses them to estimate the top of the water table[3].
Why does it say "Not reported by USDA"?
USDA has no water table value for this soil. We show that instead of guessing.
Is this a FEMA flood zone?
No. USDA’s flooding class is a soil-survey estimate[6]. Lenders use FEMA’s flood maps to decide whether flood insurance is required[7].