It is also worth considering what type of ink your tattooist is going to use,there are quite a few new types of ink on the market that actually have fluorescent colors, so if you want something original and that will be a 'masterpiece' then take some time to look into the vibrant new colors and check with your tattoo artist to see if they use them.
One of the best things to do is to download some of the free tattoo material that is available on several websites and start getting a general picture of the type of Japanese water tattoo that you want and also of those sites that sell them. Personally,I prefer the sites that let you download samples so that you can print out full size tattoos at home and get a much better idea of how it is going to look. You could even cut your tattoo out and stick it on your arm or wherever you want it to go, to give you an idea of how it is going to look.
There are also some tattoo galleries on the web that offer this download service and who also have literally thousands of tattoos available for downloading, these sites also normally have good indexing systems so it should make it fairly easy for you to check out many different styles of Japanese water tattoos.