Yes. If you don’t have a lemon to hand but you’ve got some lemon extract, use that instead. This stuff lasts forever in a bottle, and is always handy to have around. As a rule of thumb you should use half the lemon extract, when compared to the amount of natural juice you’d find in a freshly-squeezed lemon. Fresh lemons typically contain 2-3 tablespoons of juice in total. So, add around 1.5 tablespoons of lemon concentrate to your warm water.