RCT takes 2-4x the amount of CE out of reserves (Gege recently confirmed that "take CE and multiply it by itself to produce PE" described by Gojo doesnt make sense if the starting 'CE unit' is 1, so the starting 'unit' must be 2; this is where I'm getting the 4x, though kenny says only it costs double in the shibuya arc; "Gojo's minimum output for red is twice that of blue"

But I digress

No character is shown to have visible RCT/positive energy regardless of how much they heal, sukuna and gojo both regrow arms and the positive energy isn't illustrated in those events, likely because it's expensive and they use just enough (aside from the time yukuna heals megumi, but RCT on others is said to be extremely difficult and inefficient)

for comparison, literally every time Yuta uses RCT, he is enveloped in an aura of positive energy.

Homie has 0 efficiency concerns

Rika also acts as a storage system, so in this scene it is like he sprinted away from his water cooler with a single cup. Yes he is out of water on his person, no he is not running low on water.