According to what I understand, you would like to perform this experiment in a garden outside home. This experiment is possible, but the demonstration is only safe if the common sense precautions associated with the use of a portable gas stove are observed. You can only attempt to repeat this demonstration under the supervision of an adult. Do not try to do it yourself without the help of your teacher or an adult.
a) A general demonstration of the phenomena of implosion, using water, can be found in this link describing the experiment.
Here they are essentially just using water to generate the pressure gradient that will cause the implosion- so I am not sure if this is what you meant by "water implosion demonstration".
A very strict and literal interpretation of water-implosion would be collapse of the water molecules themselves, causing an inward suction process. From what I have read, this will typically result in a vortex. A vortex is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved.
Demonstrating a vortex is also a rather easy demonstration that can be done with two 2-liter soda bottles (I have just not heard the term implosion used to describe this, hence my uncertainty). Here is a decent link with instructions for this demo .
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