Is there any side effects of lemon water? is there any benefit of adding honey to it?

Bad if too much: You don't specify if you are trying to achieve a certain goal by using lemon water. I am assuming you are inquiring about drinking lemon water. In general drinking water is a safe activity, but as always there are dangers if done excessively or under certain conditions. Flavoring water with lemon juice falls into the same venue. See http://en.Wikipedia.Org/wiki/water_intoxication.

Safe & wholesome: If you believed everything you read about the benefits of lemon water -- especially sites that suggest there's a magic to adding lemon or honey over simply drinking enough water in an era when our food tends to be overly salty -- you'd be reading uncritically. If you enjoy it by all means do it. If you have health issues, use this only as an adjunct in an evidence-based program with your dr.