How to kill fleas in water. Killing fleas in water is difficult and easy at the same time. Essentially what you want to do, is you want to get yourself a large tub of water, preferably the bathtub, but this is a demonstration, so I have this little cat litter pan here, with water in it. We're going to take out animal, this is our animal today. I know it's kind of silly, but work with me here. And, you're going to take, you're going to give your, you're going to give your dog a bath, o.k. And, you want to get him submerged in the water up to his neck, o.k. No higher than that, cause you know, we don't want to make him think he's going to drown or anything. So, up to his neck, o.k. And, you want to keep him there for at least fifteen minutes and what that'll do, is that'll drown any of the fleas that are below the neckline. The other thing you can do while doing this bath is you can actually take a drop or two, preferably one, err on the side of caution, cause it's got kind of volatile stuff, but a drop or so of tea tree oil, or essential oil of lavender, either one of those can help. Of course, never apply this directly to the animal, it goes in the bath water and it gets mixed up, so we'll just put a little drop of that in there. Mix it around a little bit and you can take that and you can scrub the animals ears, and on his head, make sure you never get it in his eyes. You don't ever want to get it in his mouth. Use a washcloth if you have to, and you're just going to give him a good one. Of course, while you're doing this you can actually go through the fur on his head, and you can look for adult fleas. You'll see them, I mean adult fleas are noticeable. So, you can look through and you can crush them, or get the off the dog anyway, get them into the water so they drown. Those are the, that's how you're going to kill a flea with water. It's kind of a lot of work, it can be stressful on you and the dog. So, do it only if you have to. I'd much rather see someone using a commercial preventative repellent.