This is earth-energy. Mental energy is air-energy. The energy of thought. I find this the hardest energy to replenish, as air is not really my element. Also I play solitaire a lot.
Water energy is emotional.
Without it I get touchy. Or, if you're not feeling so generous, utterly bitchy. I use it do deal with tyrying situations, but, most importantly, to help my friends. Also, as I am strongly empathic, I use it to counteract the whirls of negative emotions that surround me. This is a constant drain.