I didn't think the article was that informative and some of its science seemed a bit muddled - how can anything have a surplus of either anions or cations? Embedded in all this though there does seem to be some clear benefits although the water is probably there usually just to dilute the lemon, as many people find it difficult to take pure fresh lemon.
I'm glad lemon juice is beneficial as I absolutely love it. And if you're ever in the Sloan Square area of London, go to the Al Dar Lebanese restaurant, where they do a fresh lemonade that's out of this world, whizzed up on the spot from fresh lemons - frosty cold, zappy with lemonyness and absolutely delicious. Had one there last night, in fact, with my tasty chicken shawarma.