Deep dive · Updated October 17, 2026

El Niño flood prevention for Marin homes, and what to do in the first hours after water gets in

This guide focuses on one thing: keeping water out of your home this winter, and what to do, hour by hour, if it gets in anyway. For the complete household checklist including alerts and go-kits, see North Bay Pros' Marin El Niño storm-prep guide. Related reading on this site: El Niño 2026 water damage prep, Marin creek flooding and your home and the first 24 hours after water damage.

The 2026–27 outlook

As of the NOAA Climate Prediction Center's ENSO Diagnostic Discussion issued October 8, 2026, an El Niño Advisory is in effect. CPC says El Niño "continues to strengthen," with a strong-to-very strong event likely through January–March 2027 (greater than an 83% chance), and the Niño-3.4 index reached +2.1°C last month. CPC also stresses that with an event this strong, the chances of typical El Niño impacts are "larger, though not guaranteed." In other words: a wet winter is more likely, not certain. The next CPC update is scheduled for November 12, 2026.

How storm water gets into Marin homes

Most storm water damage comes through a handful of routes:

• Surface runoff flowing toward the house from hillsides, driveways and neighboring lots
• Overflowing gutters dumping water against the foundation
• Rising creeks and bay-side high water, which Marin County Public Works notes can be made worse by seasonal king tides
• Groundwater seeping into crawlspaces and basements after days of rain
• Sewer backups when laterals or mains are overwhelmed

Grading and drainage: walk it in the rain

The best drainage inspection happens during a light rain. Put on a jacket and look for:

• Puddles against the foundation or under decks
• Downspouts that empty right at the wall
• Water running down the driveway toward the garage
• Clogged yard drains and catch basins
• Hillside runoff with nowhere to go but toward the house

Fixes range from simple (downspout extensions, clearing drains) to bigger projects like French drains or regrading. Note what you see now so a pro can plan it properly.

Sandbags that actually work

Sandbags are for redirecting shallow water away from doors and garage openings. They're not a waterproof wall. The county's advice:

• Buy them before a storm. The Marin County Office of Emergency Management recommends purchasing sandbags from a hardware store in advance because free supplies may run out.
• Know your nearest free site. The county keeps a current list of emergency sandbag locations across Marin. Bring your own shovel; some sites limit bags per household.
• Learn how to place them before you need them. Marin County Public Works calls knowing how to properly use sandbags a critical part of flood preparedness.

Sump pumps and crawlspaces

Marin County Public Works advises residents in flood-prone areas to test sump pumps ahead of storms and high tides.

• Test by pouring water into the pit until the float triggers.
• Clear debris from the pit and check the discharge line drains away from the house.
• Consider a battery backup and a high-water alarm.
• Check the crawlspace vapor barrier and look for standing water now, while it's dry.

Sewer backflow protection

During heavy rain, water entering cracked private laterals can overload sewers, as the San Rafael Sanitation District explains. A backwater prevention device helps stop wastewater from being pushed back into your home. Ask a licensed plumber whether you have one and whether it works. Some districts require them; Sanitary District No. 5 requires a backflow device as part of new connection permits.

Know your flood risk

• Check your address on FEMA's Flood Map Service Center or MarinMap's FEMA Flood Info tool.
• Ross Valley homeowners can review the Flood Control Zone 9 map.
• Ready.gov notes homeowner's insurance doesn't cover flooding and flood policies typically take up to 30 days to start.

The first hours after water gets in

Minute 0–15: make it safe

• Don't enter standing water near outlets, appliances or the electrical panel. Ready.gov warns of electrocution risk and advises turning off electricity only if it's safe to do so.
• If floodwater is outside and rising, follow AlertMarin instructions and never walk or drive through it.
• Floodwater and sewage can be contaminated. Keep children and pets away.

Minute 15–60: stop it and document it

• Shut the main water valve if the source is plumbing.
• Redirect runoff with sandbags or by clearing a blocked drain, if safe.
• Photograph and video every wet area before moving anything.
• Call your insurance company to start a claim. Our guide to water damage insurance claims in California explains what to expect.

Hours 1–6: get water out

• Remove standing water with a wet vac or pump.
• Move furniture, rugs and valuables to dry rooms; put foil or blocks under furniture legs.
• Pull up wet area rugs and remove soaked cushions.
• Open interior doors and cabinets to let air move.

Hours 6–48: dry it out

The EPA says it's important to dry water-damaged areas and items within 24–48 hours to prevent mold growth. If water has soaked into walls, under flooring or into the crawlspace, household fans usually aren't enough. Professional drying uses moisture meters and commercial dehumidifiers to confirm materials are actually dry. For a detailed drying timeline, see our sister site's after-the-storm drying and mold-prevention timeline.

When to call a water damage pro

• Water reached drywall, flooring, insulation or the crawlspace
• The water came from outside (floodwater) or the sewer
• You can't get things dry within a day or two
• You smell mustiness or see stains spreading

Verify any contractor on CSLB's license check.

Sources

• NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct 8, 2026
• Marin County Office of Emergency Management, Emergency sandbags
• Marin County Public Works, Prepare for winter storms
• FEMA, Flood Map Service Center; MarinMap, FEMA Flood Info; Marin County Flood Control District, Zone 9 map
• Ready.gov, Floods
• U.S. EPA, A Brief Guide to Mold, Moisture and Your Home
• San Rafael Sanitation District, Sewer Laterals; Sanitary District No. 5, Sanitary Code
• Contractors State License Board, Check a License

Frequently asked questions

This guide is general information, not legal, insurance or medical advice. Sources are linked in the text. Marin Water Damage is a referral service and doesn't perform the work.