There are a bunch of civs that do just fine in water maps. My personal favorites are Carthage and the Ottomans.
- Carthage = usefull for REXing along the coast + messenger of the gods = scientifical powerhouse. The quinquerremes are great for taking low-deffense cities in ancient era - be prepared to lose some, though.
- Ottomans = free ships. Nuff said. Build 2-3 trirremes and start capturing barb ships. I usually end up with a 10-ships fleet, wich I use to take down another civ. Specially usefull when playing again civs with a ship UU, like Carthage. (I once got 3 q-remes as the Ottomans this way, which ended up being REALLY helpful.
- England = they have the Ship of the Line, a really powerful frigate, which, allied with its UA, end up being a quite fast unit. I don't play enough England to give you advices, but they seem like a good civ for naval surprise attacks and for escorting units along an ocean.
- Byzantines = their only bonus on water maps is the Dromon, and this ranged ship can be really useful. Not my priority choice, but they can handle it quite well.
- The Netherlands = they shine when you get the Sea Beggars. Spam cities along islands to get luxuries, trade with other civs, buy sea beggars, conquer civs with different luxuries, repeat. Really powerful, IMHO, but people seem to call it underwhelming. I like it, though
- Polynesia = Wayfinding is great for settling in the best islands (specially those with a natural wonder) and for finding other civs for trading. The moais are ok for a cultural victory, and sometimes spaming them across the coast is quite helpful. The key here is to explore with your maoris for ancient ruins no one else can reach until the optics and beeline construction to pump out some moais.
- Denmark = they are all about water. Their UA gives a bonus for embarked units, which make them a powrful civ for surprise attacks down other player's coastlines. Their UUs are nice because one (Berserker) upgrades into the other (Norwegian Ski Infantry), so it can be quite helpful for amphibious, fast or rough terrained attacks.
- Korea = not the best for a water map, but the Turtle Ship can be great for deffense - and for taking down enemy cities, as it is 16 strenght higher than the caravel, which it replaces.
Those are the ones I can remember. The civs with ships UUs and sea-orientated UAs are the best for a water map, but I strongly recommend Carthage and the Ottomans, mostly because they are handly and partially because I love'em!
Also, I recommend following the Commerce policy tree - it is ALL about coasts, seas and some luxes. Getting the Great Lighthouse should be a nice - for me, it is essencial, but I think other players might disagree, and it is quite hard to get on watery higher leves. The Colossus should be good enough too. Prioritise the top part of the tech tree when you can and keep your triremes going, that's all I can say. Water maps are really funny, and naval warfare is one of the most interesting part of the game. Privateers rule!
