Will soapy water kill fleas?

I've seen videos of people using a lamp next to soapy water as a flea trap. Does this actually work?

Yes, it works — to a point. Fleas are drawn to light and heat, which they use to locate a host. Place a lamp over a shallow bowl of water with a few drops of dish soap in a dark room, and fleas will jump toward the glow and land in the water. Fleas in the water bowl can't escape and end up drowning. 

The problem is that this method only targets the adult fleas that wander into the trap. Fleas lay up to 50 eggs a day, and those eggs, larvae, and pupae are hiding in your carpets, pet bedding, and furniture, completely untouched by a bowl of soapy water. 

So while the trap might show you that fleas are present, it won't come close to solving the problem. As well as only attracting adult fleas, the trap does nothing to address why fleas are in your home in the first place. Pets, wildlife, and even secondhand items can all bring fleas indoors. Without treating the source, they'll keep coming back.

In a nutshell, home remedies like this are unlikely to make a meaningful dent. You’ll need professional flea control intervention (and a strong vet-recommended flea treatment).