Waymos Have Trouble With Floods, Which Is Surprising

Waymo's self-driving cars can't reliably measure how deep a puddle is. That's a shocking blind spot for a vehicle packed with lidar, radar, and cameras — sensors that should make water depth an easy calculation. Yet, according to a recent Forbes report, Waymo vehicles struggle with floods, raising questions about their readiness for adverse weather.

Waymo, the autonomous vehicle subsidiary of Alphabet, has been testing robotaxis in Phoenix, San Francisco, and Los Angeles. Despite years of development and millions of miles driven, the company's vehicles have shown difficulty in accurately sensing the depth of standing water on roads. Flooding can be deadly: a submerged road can hide debris, trap a car, or cause hydroplaning. For a fleet that prides itself on safety, this vulnerability is a significant concern.

The issue came to light in a Forbes article titled "Waymos Have Trouble With Floods, Which Is Surprising." The piece notes that Waymo's 3D sensors — lidar (light detection and ranging), radar, and high-resolution cameras — should theoretically measure water depth by analyzing reflections and surface geometry. But in practice, the sensors often misinterpret water as a solid surface or fail to detect depth altogether. This is not a trivial edge case; floods affect millions of drivers annually.

Waymo's trouble with flood detection is surprising because the company has long claimed its sensor suite can handle all conditions. Lidar emits laser pulses that bounce off objects; radar penetrates fog and rain; cameras provide visual context. Yet water's reflective and refractive properties confuse these systems. For example, lidar may see a mirror-like surface and treat it as ground, or radar may scatter off ripples, giving false depth readings. Waymo has not publicly detailed its failure rate, but the Forbes report suggests it is enough to cause operational setbacks, such as rerouting or pausing trips during storms.

Industry observers note that this is not unique to Waymo. Tesla's vision-only system has faced criticism for handling puddles and heavy rain. Cruise, another autonomous rival, has reported similar challenges. However, Waymo's seniority and Alphabet's resources raise expectations. "If anyone could solve water depth perception, it should be Waymo," said Samir Patel, a robotics researcher at MIT. "The fact that they still struggle indicates the fundamental complexity of this perception problem."

The broader implication for autonomous vehicle safety is clear: any system that cannot reliably assess flood depth is not truly weather-proof. Regulators in California, where Waymo operates, have noted that heavy rain and flooding are common. The company may need to develop dedicated flood detection algorithms, use ultrasonic sensors, or even integrate data from weather services to preemptively avoid flood-prone areas.

Looking ahead, Waymo will likely roll out software updates to improve its flood detection capabilities. The company is also testing vehicle-to-everything (V2X) communication that could relay road condition data to its fleet. Meanwhile, competitors will watch closely: the first company to reliably handle floods will gain a significant safety advantage. For now, any Waymo user caught in a downpour should be cautious — their robotaxi might not know how deep the water really is.