How do I explain salt water conductivity to a child?

How about a visual demonstration? Here is a link to one that can be done at home.

Edit: It still needs to be explained why someone would need to know this. Are there any examples you can offer? Starting off with a real life story that someone (child or adult) can relate to helps the learner understand why it is important to know the fact, not to mention how it works.

All molecules are held together by electric forces. Normally water molecules don’t conduct electricity very well because they are mostly neutral. When salt crystals dissolve in water, however, salt molecules come apart as they mix with water molecules, and (in the case of salt) each molecular piece carries an electric charge rather than being neutral.

It follows that saltwater conducts electricity well because there are abundant charge carriers—namely the salt ions such as Na+ and Cl-. (This differs greatly from metals, where a sea of free electrons are the charge carriers.) This is important because animal cells, like neurons and muscle cells, generate and conduct electricity using salt ions, i.e., “saltwater.” Usually biological voltages are minuscule but don’t grab an electric eel!

Later she can learn about ionic bonds & compounds, and electro-chemistry etc.

Here is an experiment you can do with your child.

I didn’t fully understand it myself until I was in high school and I understood the concept of ionization.

why would a child ever want to know about saltwater conductivity? can’t you just simplify it until she is a teenager? Say that salt makes water ‘more electric’ and then explain it all in more detail when she’s older (if you are still driving her dogmatically on the road of life that is “master of saltwater conductivity knowledge”),

It was for a project that she was doing, she’s already done the experiments and everything. She still doesn’t get it though.

@SvetlanatheGreat I’ve seen some appallingly bad scientific explanations that appear in online educational materials and even some textbooks. I think the central lesson is that electrical current is the flow of electrical charges. Saltwater has lots of charged particles (ions) that strongly conduct electricity, while pure water has few charged particles and manages only a weak current. Conductivity measures this ability to conduct a current between electrodes immersed in the liquid.