When was the last time you needed to plug something under water? Seriously.
Products like this encourage people to do stupid things like blow dry their hair in the bath tub. Have you ever seen the warning labels on a hairdryer? "Do not use under water. Do not use while sleeping." There are warnings like this because some moron has tried it and sued the company when they electrocuted themselves or caught their hair on fire.
There's absolutely no justification for this product.