Jor-El and Jax-Ur both explicitly link Kal-El’s strength to radiation. Jor-El uses the metaphor of drinking to describe the absorption and storage of solar radiation (first in speaking with Lara and then again to Kal-El). One isn’t hydrated only while drinking, but also while relying on one’s stores. However, a better metaphor- which accounts for the Kryptonian Atmospheric weakness- would be a device, like a laptop, with a removable rechargeable battery which can also be plugged-in.
The device can draw from either a charged battery or the plug.
Being in sunlight is drawing power from the plug. However, Clark still exhibits powers at night, when he can draw from his battery.
What Kryptonian Atmosphere inhalation removes access to the battery, like taking a removable battery out. Taking it out doesn’t cause the battery to completely discharge (the battery isn’t drained) and you don’t lose power so long as you are still plugged-in. However, if you aren’t plugged-in and the battery is out, you lose power. If the battery is put back, power is immediately restored, the battery doesn’t have to be recharged.
This metaphor is consistent with everything we see in the film.
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Man Of Steel Answers Insight Commentary (MOSAIC) Podcast covers these kinds of questions and more in depth for fans of Man of Steel and those excited by the DC Cinematic Universe.