September 2025
By: Josh Walejewski
Read Time: 2 Minutes

Southeastern Wisconsin saw record flooding on Aug. 9–10, 2025, after hours of torrential rain. Northern and western Milwaukee County, and Eastern Waukesha County, including Wauwatosa, West Allis, Menomonee Falls, Elm Grove, and New Berlin, were hit the hardest.

Some areas reported an excess of 14 inches of rain, making it the second-wettest two-day total on record for Milwaukee, even triggering emergency declarations in many of the areas impacted.

According to recent Impact 211 data, over 21,000 damage reports have been filed by residents. FEMA assessments estimate about $33 million in home damage and $43 million in damage to public infrastructure.

Events like this remind us that while you can’t control the weather or completely floodproof your home, you can reduce the odds of a basement disaster. Here’s a quick guide on what can be done to help protect your home—focused on what actually works for Southeastern Wisconsin homes.

Identifying Threats Before the Storm

It’s crucial to identify flooding threats and to understand how water can enter your home/basement. Basements usually flood in two main ways: (1) the city sewer surges and sends water back up through floor drains, or (2) groundwater around your foundation rises and seeps in. Figure out which one you’re dealing with—the protection plan is different for each.

Homes Connected to City Sewer/Storm Water Systems

Most homes impacted during the August floods are on a municipal sewer/wastewater system. When your home is connected to a municipal sewer, one of the biggest threats you face is from floor drains backing up in your basement.

Floor drains are designed to carry water from your home through underground pipes to the city system. However, when the city’s system is maxed out during torrential rains, that water will look for the path of least resistance to flow. Unfortunately, that path can become a home’s floor drain connection to the city sewer. The result is your floor drain(s) erupt like a geyser.

Preventing City Backups & Floor Drain Geysers with Backwater Valves

Your best defense is a backwater valve installed on your home’s main drain line. When the city system isn’t maxed out, the backwater valve stays open so your plumbing works as usual. However, when the city main surges occurs, the valve shuts and blocks the reverse flow that would turn floor drains into ‘Old Faithful’.

Keep in mind, during flooding events—when the valve may be closed, limit water use (toilets, showers, laundry) so you don’t back up your own pipes as water will not be able to leave your home.

Also note, this protects against sewer surges only; groundwater threats still require a working sump system. Kettle Moraine Plumbing Services can quote and install backwater valves if your home doesn’t already have one.

Groundwater Threats & Sump Systems (Non‑Sewer)

Groundwater presents different threats compared to sewer backups. Overly saturated groundwater can seep into your basement from the soil around your home’s foundation.

When Groundwater Problems Typically Show Up

Groundwater entering your basement often occurs during periods of heavy and/or prolonged rain events (like Aug. 9–10, 2025). Spring is also an important time to make sure your sump pump system is in working order. According to the National Weather Service, April, May, and June have the highest rainfall averages. If there is still snow on the ground and a rain event strikes, it’s a perfect recipe for water in the basement.

Why it happens

When soil around the foundation becomes saturated, hydrostatic pressure causes water to push through the home’s foundation. Water usually enters through the cove joint (where wall meets slab), block cores, or other gaps/cracks.

Compromised drain tiles can also be a culprit. When drain tiles are clogged or broken, it’s unable to collect and route water to the sump. Additionally, an undersized sump pump/basin might not be able to keep up with incoming water. Sump pump discharge pipes, whether frozen, clogged, crushed, undersized, or routed incorrectly, can also cause water to flow back towards the foundation.

How to Safeguard Your Home against Groundwater Threats

Have a professional check that your existing system is sized and designed correctly
Install a sump pump with battery backup in case the grid goes out
Add a high water alarm with phone notifications
Install a high capacity dehumidifier to remove moisture post flood
Install a whole home generator
Make sure downspouts extend at least 4-6 feet from the home.

Bonus tip: Most homeowners do not like looking at or mowing around downspouts that stick out more than a few feet. However, it’s critical to keep the ground around your home from becoming too saturated. At a minimum, downspouts should extend 4-6 ft from the home, but 10-15 ft is considered best practice.

If you absolutely can’t stand having downspouts that extend that far out, consider digging a trench and running some 4” pipe underground that can safely move water away from your home while keeping things aesthetically pleasing. Just be sure to call The Diggers hotline before getting started if you plan to DIY.

Final Takeaways

While you can’t control the storm or completely floodproof your home, you can control the weak links. If you’re on city sewer, a serviceable backwater valve is your best defense. If groundwater is the culprit, a correctly sized and designed sump pump system, clear discharge, solid grading, and adequate extensions on the downspouts can make all the difference.

Want a professional opinion? Our plumbing team is here to help. Give our office a call today.