Designing Your Landscape to Absorb Water Naturally: The "Sink It" Strategy

Sinking water—also known as infiltration or percolation—allows rainwater to pass through your garden soil rather than rushing off into storm drains. This natural process reduces downstream runoff, filters pollutants, recharges groundwater supplies, and improves overall water quality. It's the final step in the sustainable stormwater mantra "Slow it, spread it, sink it," following the crucial first two phases of slowing water down and spreading it across the landscape.

Fulcrum Structural Engineering

How Infiltration Works

Infiltration is a vital natural process where water absorbs into the soil and percolates downward, becoming cleaner as it travels. Organic matter in the soil acts like a sponge, holding moisture and filtering contaminants. The "sink it" phase builds directly on slowing and spreading water, because water that's already been slowed and dispersed across the ground surface infiltrates far more easily.

Using your soil's natural absorption capacity is the simplest approach, but challenges arise when soils have low infiltration rates. Some soils lack the physical structure or chemical capacity to handle significant stormwater volumes. Even with poor infiltration, you can still sink water onsite by amending soils in rain gardens and swales to boost their absorption capacity. Determine your soil's infiltration rate using the USDA soil survey, which provides measurements in inches per hour for your specific property.

Permeable Hardscapes: The First Line of Defense

Fern Ridge Landscaping

If you have adequate space and decent soil infiltration, sinking water directly into the ground becomes the natural third step. One of the easiest surface-level improvements is incorporating permeable materials into hardscaped areas—driveways, walkways, and patios. Effective permeable options include:

• Gravel
• Wood chips
• Permeable paving systems

Beyond hardscapes, consider how planted areas can enhance infiltration:

• Meadows and grassy perennials
• Beds of water-loving plants

Green Roofs: Dual-Purpose Water Management

Prentiss Balance Wickline Architects

Green roofs excel at both slowing and sinking water. Shallow extensive roofs planted with sedums can absorb an inch of rainfall during small storms, releasing it back through evapotranspiration. Deeper intensive green roofs infiltrate even greater volumes, making them powerful tools for rooftop runoff management.

Strategic Planting Beds for Absorption

The Garden Consultants, Inc.

Rain gardens effectively absorb large runoff volumes but require significant space. When space is limited, a series of planted infiltration beds can achieve similar results. Several planting combinations work beautifully for stormwater absorption, adaptable to various climates and site conditions:

• Grassy meadows and prairies with diverse root structures—taproots, bulbs, deep roots, and surface-spreading roots—can replace conventional lawns in full sun to dramatically increase infiltration.
• Dense, multi-stemmed water-loving trees and shrubs thrive in shady areas and provide privacy while absorbing runoff.
• Shaded ferns and mosses flourish in high-organic-content soils.
• Dense, layered plantings combining groundcovers, woody shrubs, herbaceous perennials, and trees create powerful infiltration zones. Simply adding more native plants to existing beds or establishing new layered plantings along property edges works remarkably well.

Bioswales: Engineered for Maximum Infiltration

David Thorne Landscape Architect

While standard swales primarily move water, bioswales are specifically designed for infiltration. Fully planted for water absorption, they feature engineered soil mixes that maximize percolation. Specifications vary based on native soil and local regulations but typically include coarse sand and compost blends.

Small-Space Solutions

ZDA Inc.

Sinking water in compact spaces or low-infiltration soils requires creative design. Even without room for bioswales or large rain gardens, you can infiltrate water through:

• Planted infiltration beds—narrow strips between hardscapes that function as miniature rain gardens, capturing runoff from adjacent impervious surfaces.
• Stormwater planters—containerized rain gardens that capture and absorb roof runoff.
• Subsurface infiltration systems like dry wells that temporarily store water and slowly percolate it through amended surrounding soil.