Janet Balaskas is the author of the classic childbirth book Active Birth. Less well-known is her also excellent, The Waterbirth Book, which was published in 2004. In this book, Janet Balaskas offers a comprehensive & inspiring guide to waterbirth for both parents & midwives. Her book is detailed, straightforward, and supportive.
The book contains sections about historical and cultural perspectives of waterbirth, the benefits of water in labor and birth, what to expect and how to prepare for a waterbirth, personal stories, how to choose and use a birth pool, information about the use of water during each stage of labor, and specific information/instructions for midwives.
The Waterbirth Book is quite good, comprehensive, and informative. It also has some nice black & white photos. It is very up to date. It is geared toward a UK audience, so some of the language/stats are based on that audience (for example, it assumes that midwives are legal & that one will readily be present at your birth--I wish the same were true in all US states!).