Question

We had a project in high school before, that was 24 yrs. ago.  This project was the most electric conductive liquid solutions by dropping two rods on it, but I don't remember any of the liquids.  Can you tell me what makes water more conductive with electricity by adding any kind?

Answer

Water (pure water) normally has very very low conductivity (none if you talk to some people).  This is because water is a covalent liquid.  The ions are held together by sharing electrons.  Most covalently bonded liquids are not electrically conductive because the electrons, which essentially act as the medium by which the electricity travels, are tied up between the atoms they are related to.  A small amount of water does ionize:

2H₂O <----> H₃O⁺ + OH^-

This ionization is more characteristic of ionic bonds.  Ionic bonding often occurs between metals and non-metals.  Ionic solids have the characteristics of a high melting point and low vapor pressure among other things.  The reason I am going off toward the subject of ionic solids is because these solids when dissolved in water increase the number of free ions which do exactly what you're asking, they increase the conductivity of the water.  For example, epsom salt (magnesium sulfate):

MgSO_4(s) --(H₂O)--> Mg²⁺_(aq) + SO₄^2-_(aq)

In ionic bonded materials like magnesium sulfate above, the electrons in the solid are essentially given from one atom to another (as opposed to covalent bonding where the electrons are shared).  Because of this when the solid dissolves the atoms are free to go in their own directions, this allows electrical current to leap frog through the solution along the ions present, increasing the conductivity of the solution.

So, dissolving anything containing an ionic bond in water will increase the conductivity of the solution because it will ionize.  Covalently bonded molecules will not really increase the conductivity because they do not ionize, for example, sugar:

C₆H₁₂O_6(s) --(H₂O)--> C₆H₁₂O_6(aq)
Sugar is the usual example but this also includes alcohols like ethanol.

Regardless, ionic bonded substances will increase conductivity such as Sodium Chloride (NaCl - table salt), Magnesium Sulfate (MgSO₄ - epsom salt), Sodium Bicarbonate (NaHCO₃ - Baking Soda) and a number of other solids.  Acids and bases will also increase the number of ions in solution by generating hydrogen or hydroxyl ions and the respective anion or cation associated with it.