1)
What is the danger of drowning?
1.
Radak, Malbim: This is like verse 3 says - "Tavati bi'Yven Metzulah."
2)
What is the danger "mi'Son'ai umi'Ma'amakei Mayim"?
1.
Radak 1 : These are the Mashal and the Nimshal. The prefix Vov in umi'Ma'amakei equates, like "Mayim Karim Al Nefesh Ayefah u'Shemu'ah Tovah me'Eretz Merchak" (Mishlei 25:25), like I explained above (68:35). I should be saved from my haters like from deep water. I.e. my haters are like deep water.
2.
Malbim: This is like it says "Basi v'Ma'amakei Mayim", "Rabu
1
In some texts, this is in his Perush on verse 16.