on the water 在水上
这里on和in的意思是不一样的
如果是船，就要用on，表示在水面上
如果是人游泳，就要用in，表示在水中
in the water 【在水中】表示大部分或全体在水面以下。如：
He let his fingers trail in the water.
他把手伸进水里，任水流滑过指间。
来自柯林斯例句
minute amounts of chemicals in the water
水中含量极小的化学成分
on the water【在水上】表示【大部分或全体在水面之上】。如：
The whirlpool sucked down everything floating on the water. 漩涡把水面上漂的东西都吸进去了. 来自《简明英汉词典》
The moonlight gleamed on the water.
月光照在水面上泛起粼粼波光。
来自《权威词典》
鸭子在水里游，得看具体情况，如表示【潜水】用in the water.如表示【在水面上荡漾】用on the water.
鸟在树上用"in"
in the tree和on the tree译成汉语都是“在树上”之意,但所表示的含义是不一样的.in the tree多指外界的事物或人在树上,而非树木自身所长；而on the tree则多指树自身所有,长在树上的东西.请辨明：
树上有一些鸟.
误：There are some birds on the tree.
正：There are some birds in the tree.
树上（长）有许多又大、又红的苹果.
误：There are many big,red apples in the tree.
正：There are many big,red apples on the tree.
waste water释义：
污水，废水
例句：
Waste water is pumped from the factory into a nearby river.
工厂里的污水被抽到了附近的河里。
词组：
wastewater treatment污水处理
wastewater disposal废水处置
wasted water释义：
浪费水
例句：
The proportion of fee to deal with wasted water and water resource is too low.
水价构成中成本不实、水资源费和污水处理费比重偏低；
in the water bar 释义：
在水吧里
例句：
A few minutes later, Tom was in the shoal water of the bar, wading toward the Illinois shore.
过了几分钟，汤姆来到沙洲的浅水区，涉水朝伊利诺斯州的海岸走去。
at the water bar释义：
在水吧
例句：
The evidence may be circumstantial at first — say, spectral bar codes of interesting molecules like oxygen, ozone, methane and water — and leave room for alternative interpretations.
最初的证据可能是间接的——比如说，类似氧气、臭氧、甲烷和水这类物质有趣的分子的光谱条形密码——为日后可供选择的其他解释留有余地。
fresh water plain water没有区别。都表示“淡水 ，白开水”的意思。
许多水的表达是a lot of water, much water或者plenty of water，但是不能用many water，因为water是不可数名词，而many只能修饰可数名词，后面加可数名词复数，much只能修饰不可数名词，a lot of＝lots of＝plenty of都表示许多的意思，后面加可数名词复数或者不可数名词。
salt water作形容词,只作定语,表示“含盐的”或“用盐腌制的”,如：salt water （盐水）,salt pork（腌制猪肉）
salty water作形容词,既可作定语,又可作表语,表示“咸的”.如：The bacon is too salty for me.
If you want some more salt,just sprinkle some on them.
这里的salt是名词,意为“盐”.如果你还想加点盐，就撒一些在上面。
区别就是两者都是合成词+water的短语，具体的不同如下
spring water中文意思是泉水
It is a kind of hot spring water, which contains the mineral base, to restore and transform it into weak alkaline water.
pure water中文意思是[化学] 纯水，净水；纯净水
The bottle is sealed, and the label says "pure water".
tap water:从管道通过水龙头的水.potable water:是可以喝的水.像 矿泉水如果tap water被消毒了的 那它也是potable water
boiled water是已经滚开了的水，而boil water则是烧开水的意思，区别可以从以下例子看出：
There is not much boiled water left, can you please boil more water, so we have enough water to supply. 烧开的水已经不多了，请你多烧点水，我们有足够的水供应。
区别就是两者都是动词boil非谓语动词+water短语但意思是不一样的，具体的不同如下
boiled water中文意思是白开水；煮开过的水
If you give your baby juice, dilute it well with cooled, boiled water.
boiling water中文意思是沸水；麻烦事
His mother laughed, put some Elder-flowers in the tea-pot, and poured boiling water upon them.