We still need a lot of work to do to make our city can even more rightly be called a city with a blue sky, clear water, green land and a beautiful environment.

如果翻译成the sky will be bluer, the water will be clearer, and the land will be greener, 那么它就有可能暗示：天原来不是蓝的、水不是清的、地不是绿的, 而且这三个比较级的形容词可以理解为“只是有所改善”，力度不够。但实际上我们要表达的意思现在就是天蓝、水清、地绿；到将来的情况是天还要更蓝、水还要更清、地还要更绿。在经过了这样的深层次的理解之后，我们就可以换个角度来进行翻译：
We still need a lot of work to do to make our city can even more rightly be called a city with a blue sky, clear water, green land and a beautiful environment.