This is the 10054th most frequent Japanese word.
透き通っ
Clear; transparent.
Here, "透き通っていて" describes the transparency and clearness of the lake's water.
湖の水は透き通っていて、底が見えるほどだ。
The lake's water is so clear that you can see the bottom.
In this sentence, "透き通った" is used metaphorically to describe the purity and clarity of his voice.
彼の透き通った声がホールに響き渡った。
His crystal-clear voice echoed through the hall.
"透き通る" emphasizes the glass's inherent transparency and shine.