Which is better for fat loss?

hot lemon water

Neither one is going to make the slightest bit of difference.

What kind of hoodoo is this?

Lemon juice does NOT make you lose body fat.

There is no significant temperature. Your body will warm up the cold fluid so it may require an extra few calories of energy for that to happen, but overall you won't see any difference in your rate of fat loss if you drink all cold or all warm drinks, with or without lemon.

warm lemon water