Why Counter waves are being produced in water? While studying water waves in a cuboidal tank, the following observation was made.
A gentle tap on one side (A)of the tank, generated waves from that side towards the opposite (B). At the same instant, a counter wave was generated from (B) end of the tank towards (A). Why? Thank you!

 A: When you tapped side $A$ a pulse was produced inside the material of the tank which travelled at a speed much faster than the water waves to end $B$.
That pulse obviously disturbed the water at end $B$ to cause the waves emanating from $B$.  
A: Wave Mediums
The nature of waves is so a form of motion that occurs. The manifested ability of the wave gets classified by it's ability. For a wave is so a wave.
The major division in classification of the waves ability


*

*Medium of transmission of the mega power(matter waves) - Mechanical Waves

*Medium of transmission among, with, and around the mega power(matter waves) - Electromagnetic Waves


Mechanical Waves
A mechanical wave requires an initial energy input, however let us not forget the amazing amount of already present energy that we find within the medium we call matter. The energy manifesting the matter already fluctuates into/from a specific pattern. That it's the pattern of energy that's manifesting to what we recognize as matter.
Pattern Manifestation
We can define the pattern as the abjunction and abjuration of the strong nuclear force. Yet let us not forget that the pattern of itself exists as a wave.
The Patterns resting position
Without additional energy input the wave pattern manifests to a resting position sometimes referred to as the equilibrium position. When an object is positioned at its equilibrium position, it is in a state of equilibrium, experiencing a balance of forces.
With application of force to the Wave Pattern
This force disturbs the equilibrium and the Laws of Motion apply then to the pattern. Like any moving object, the motion of a vibrating object can be understood in light of Newton's laws. According to Newton's law of inertia, an object which is moving will continue its motion if the forces are balanced. Put another way, forces, when balanced, do not stop moving objects. So every instant in time that the pattern is at the equilibrium position, the momentary balance of forces will not stop the motion. The pattern keeps moving.


The Dampening effect
Eventually the pattern returns back to its equilibrium position if loss of energy. Also helping to define the equilibrium position as the state of the pattern that energy balance occurs.
Water for Example
At a specific temperature allowing the liquid state. The equilibrium of the pattern allows a liquid state. However if energy (in this case heat energy) dampens from the wave pattern to a freezing temperature then the wave pattern manifests as a solid.
As a note of appreciation: The tank idea ends up acting as a wonderful example of Newtons Law : Every action has an opposite and equal reaction. Yet in larger scale of the Law. Observe to see if the other side of the tank gets tapped =). 
