Great! A lot of things you just pointed out were exactly what I pulled him up on! The purpose of my posting that and allowing you to critique it was to make you see for yourself that you do know what you're doing. Negative Knight is a sensei, yet, as you can see from the above post, even he didn't know all this stuff to start with. You just have to believe you can do the stuff and that you know the stuff and the chances are you do.
Anyway, back to business. Here's my post to follow up his own. If you have any questions after I've posted it, feel free to ask.
1) Exactly, water jutsu in this terrain forms wet sand, a heavy, relatively dense substance than can be used in conjunction with your earth jutsu. Explain your moves right and you can have earth jutsu which blind your opponent as the wet sand not only inflicts blunt damage but it breaks up on impact and can effect the senses. When sand is infused with water whilst in the air, the water becomes thicker and more damaging, the water also spreads the sand on impact again look to aim for the opponents senses.
2) While its true that the trees will form as you put it a 'natural dam'. The water in these areas seeps into the earth and sets the grass and dirt, forming mud. Mud as you learn and know all too well is slippery and can assist you against certain people extremely well. Water possesses an often over looked level of brute strength, a large amount of water can easily knock over and drag along a human being, flood/ tidal waves are actually the most catastrophic of the commonly occurring natural disasters. You can use this strength to push your opponent against trees or into traps that you laid earlier.
3) Being sea, obviously this gives you means to use your most powerful water techniques instantly as you have an already developed water source. Something that people tend to forget about water however is that although they don't all require a water source, they can all use one. There are a few techniques which state that the user begins by creating a water source, if you have a water source already, you can skip through this part of the technique, allowing youth utilise the jutsu quicker, starting from the second stage of the technique. Even if water jutsu don't state this, they will ALWAYS happen quicker if used from a source. (Ill cover the development of water sources soon enough

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4) i actually disagree with your statement here, in my opinion Water on the ground in these areas will automatically be absorbed into the ground slower than if the water is settled on a field for instance. Think about when it's raining, puddles are far less likely to form on fields than in the middle of a street. Dirt and grass are naturally absorbent of water whereas water will merely sit atop of rock. Remember also, rocks are loose pieces of the environment and can be picked up by water techniques to cut and pierce, thus adding damage to what would normally merely be blunt. In this same vein, water can carry Kunai, essentially hiding them inside streams as you spit.
As a water user your best friend will be techniques like great water colliding wave, anything that can make a water source for you, without necessarily saying it makes a water source. Although relatively obvious, some people tend to disregard the water from said techniques once the technique is over, again, my like most RP, Waters power comes from description.
As well as the physical effects, think of the effect of water when you get out of a swimming pool. If your clothes are wet you are naturally going to feel heavier and you will move slower, if you have water in your ears, your ears will ring and sounds will become distorted. Water in your eyes and they sting, water swallowed in large amounts will make breathing difficult and will cause the opponent to cough and sneeze if inhaled through the nose, again, it's all in the description. If you say, the water travels toward your face. Add that this would make it incredibly hard to avoid inhaling or swallowing, add that the water would splash, sending vast amounts into the nostrils, causing coughing and irritation to the eyes. If you don't, your opponent will certainly not do it for you.
Something very simple, layer the ground with water, and it becomes near impossible for the opponent to sneak up on you. When they get close the ground would either make a splash, or a squelch or whatever sound you like... Either way, it alerts you. This works both ways, you can use the sounds that water makes as a diversion tactic, drawing your opponents attention with a carefully placed rock.