What is Ketchup?
Ketchup is a condiment sauce meant to be used in foods. Generally, they're used on several types of foods such as the iconic hotdog, mainly used on and for hot foods. Think of McDonalds and their Happy Meals with their hamburgers and french fries and put ketchup on them.
Back in the day, the Chinese composed it out of pickled fish and spices while calling it kôe-chiap or kê-chiap. It made it's way into Malaysia where the colonist from England tasted it and took it into the American Colonies while calling it Ketchup.
The standard ketchup is made out of tomatoes, vinegar and with potential addons such as onions, allspice, coriander, garlic, cloves, cumin, and mustard.
What is it not used for?
Ketchup can be misused for various things. The type of foods you don't generally see it on is fish, most asian dishes since they use sriracha sauce, and do not mix it with mustard or guac since it will lose it's taste.
For non-foods, do not use it for fake blood, do not use it as whip cream for throwing pies at people, don't use it as makeup, and do not use it as ammo for your firearms. Do not get it on your clothes since it'll be a big pain in the butt to get rid of and importantly, do not get it on your white shirt and bleach will not help you if it stays there too long.
Who in the world would use ketchup for any of those examples above. I mean, you could use ketchup as blood for acting.
Ketchup and water
You're wondering what happens when ketchup and water mix like female and male chromosomes do to make a offspring. Basically, if you refer to what ketchup is not used for then you would know that with a good mixture then you can make fake blood for acting - it is too bad that they use special effects for most films nowadays.
Considering that there no research subjects of ketchup being used with water, we're going to settled down with the Cartesian Diver bottle trick.
To put in a term sentence or two, it can float when the bottle isn't pressed and it sinks when it has been pressed. Though, it is basically in a packet and acts like a switch for a light, nooooo..