Water fasting is incredible healing tool! It can probably go deeper than juice fasting. But I wouldn't recommend it to everyone, especially to newcomers in the plant based lifestyle and without someone to guide them. It can be quite a challenging, draining experience if done for more than 3 days.
Juice fasting is more suitable for modern lifestyle because you have plenty of energy to do the daily tasks. There's also a nice documentary about it called Fat, sick and nearly dead. :)