Respiration is the action of breathing which is a process in living organisms involving the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.
An organism occurs through any stimunilation of the galnnis but respiretion cannot occur at all if it is spelt incorrectly. However, when spelt correctly, respiration is required to produce the tremendous enernigy reiquired by an organism.
Cellular respiration takes place in the cells. The carbon dioxide is released and replaced by oxygen.
The quickest way is to heat it up. You'd want a thermometer to help validate that gases are leaving the water and it isn't boiling (just check that the temperature is below 100oC), but if you see bubbles at those lower temperatures, it's air. Alternatively, just leave a glass of water out for about an hour. Those bubbles you see on the inside of the glass were dissolved air.