Water is a weak electrolyte and therefore it does not dissociate easily such as strong acid or base. Water molecule ionizes to a small extent to give hydronium ion (H3O+ and OH-) ion.
Therefore pure water also have small amount of ions. So pure water has a small but measurable electrical conductivity (a current can flow in water due to existing of ions).
Amphoteric behavior means, a compound can act as an acid and base. According to the "Lowry bronsted concept"
Now we know pure water also have H3O+ and OH- ions.
Now we consider, behavior of HCl and H2S with H2O. Water molecule accepts a proton from HCl and hydronium ion is formed as the result.
Hydrochloric acid (HCl) is a strong acid and dissolve very well in water. One electron pair of oxygen atom of water molecule attacks H atom in the HCl molecule because that H atom is positively polarized. So HCl dissociates completely by giving H3O+ ion and Cl- ion. In this example water molecule behave as a base.
Water molecule donate a proton to the base to form hydroxyl ion.
Ammonia takes a proton from water molecule and forms ammonium ion (NH4+) and hydroxyl ion (OH-).
Water is a polar covalent compound. It dissociate slightly in water to H+ and OH- ions. Due to exist of H+ ion, it shows acidic characteristics. Also due to exist of OH- ion, it can take H+ ions to show basic characteristics.
Water can react with both acids and bases like other amphoteric elements and compounds.