Stormwater and drainageGuide

Slow it, spread it, sink it: keep rain on your land

By The Downspout · Updated Oct 11, 2026 · 2 min read Share

Slow the rain down, spread it out, and let it soak in. The Sonoma Resource Conservation District says this protects your property and refills groundwater.

The idea

Old building habits sent rain off a property as fast as possible. The Sonoma guide says to do the reverse. Slow it. Spread it. Sink it. Store it.

Walk your property in the rain

• Wait for one or two storms over half an inch.
• Walk the property and sketch where the water goes. Use arrows. Take photos.
• Look at five zones: roofs, raised structures, walkways and patios, driveways and parking, and bare soil or planted ground.
• Find your septic tank, leach field and replacement area. Keep all three clear.

One inch of rain on a 1,500 square foot roof makes about 1,000 gallons. Try the rain catch calculator for your roof.

Easy first moves

• Point downspouts at planted ground, not the driveway.
• Space downspouts 20 to 50 feet apart.
• Along the drip line, lay at least 3 inches of mulch or washed rock.
• Slope the ground at least 5 percent away from the foundation for the first 10 feet.
• Add a rain barrel. See are rain barrels legal in California.

Bigger moves

• Rain garden. At least 10 feet from the house. At least 40 feet from septic systems or steep slopes. It should drain within 72 hours.
• Swale. A planted ditch that carries water slowly. It needs at least a 2 percent slope. A level swale on contour does the opposite job and holds water. See our guide to swales.
• Infiltration trench or pit. The guide says to hire a professional. Keep it no deeper than 3 feet. It needs pretreatment so it does not clog.

Watch-outs

• Never send water toward a septic system.
• Call 811 at least two working days before you dig.
• Standing water should not last more than 48 to 72 hours. Cover barrels with 1/16 inch mesh.
• Clay soil and high water tables are poor sites for soaking water in.
• Some of this work needs a county permit. See when you need a permit to change drainage.

Why it matters for groundwater: can your yard recharge groundwater?

Related reads

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