---
source: https://iinventedlight.com/library/notes/infiltration.md
title: "Infiltration: how rain soaks into the ground"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: USGS, Infiltration and the Water Cycle, US government work, public domain; USGS, Groundwater Flow and the Water Cycle, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "earth science: water cycle"
tags: ['usgs', 'water-cycle', 'infiltration', 'groundwater']
sources:
  - id: S1
    title: "Infiltration and the Water Cycle"
    publisher: USGS
    url: https://www.usgs.gov/special-topics/water-science-school/science/infiltration-and-water-cycle
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Groundwater Flow and the Water Cycle"
    publisher: USGS
    url: https://www.usgs.gov/special-topics/water-science-school/science/groundwater-flow-and-water-cycle
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Infiltration: how rain soaks into the ground

**Answer:** Infiltration is the movement of part of the water that falls as rain and snow into the subsurface soil and rock. How much infiltrates depends greatly on multiple factors.

## Where the water goes

Some water that infiltrates will remain in the shallow soil layer, where it will gradually move vertically and horizontally through the soil and subsurface material. Some of the water may infiltrate deeper, recharging groundwater aquifers. Water may travel long distances or remain in groundwater storage for long periods before returning to the surface or seeping into other water bodies, such as streams and the oceans.

## What controls it

- **Precipitation:** the greatest factors controlling infiltration are the amount and characteristics (intensity, duration, etc.) of precipitation that falls as rain or snow.
- **Soil characteristics:** some soils, such as clays, absorb less water at a slower rate than sandy soils. Soils absorbing less water result in more runoff overland into streams.
- **Soil saturation:** like a wet sponge, soil already saturated from previous rainfall can't absorb much more.
- **Land cover:** vegetation can slow the movement of runoff, allowing more time for it to seep into the ground.

## Underground rivers?

Underground rivers are pretty much a myth. Generally, water underground is more like water in a sponge: it occupies the spaces between soil and rock particles. If the water flows through the rocks easily enough to be pumped and used by people, the formation is called an aquifer.

## Claims
- id: C1
  claim: A stream can act as a direct funnel into groundwater.
  source: S1
  evidence: "a stream can act as a direct funnel right into groundwater!"
- id: C2
  claim: Some infiltrated water may recharge groundwater aquifers.
  source: S1
  evidence: "Some of the water may infiltrate deeper, recharging groundwater aquifers."
- id: C3
  claim: Water underground is more like water in a sponge.
  source: S2
  evidence: "Generally, water underground is more like water in a sponge."

## Sources
- [S1] Infiltration and the Water Cycle. USGS. https://www.usgs.gov/special-topics/water-science-school/science/infiltration-and-water-cycle . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Groundwater Flow and the Water Cycle. USGS. https://www.usgs.gov/special-topics/water-science-school/science/groundwater-flow-and-water-cycle . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).