Hot water and lemon juice is often recommended on detoxes as a way of boosting liver function. You're supposed to have it first thing in the morning before you do anything else.

It's something I was doing even before I started low carbing. I can't be bothered with buying and squeezing fresh lemons, so I use a "10 count squeeze" of bottled lemon juice instead I measured it one day and it was about one teaspoon of juice, amounting to less than 1g carb.