At first, the water felt cold. (Para. 5)
Meaning: At first the water was cold (or Sandy could feel that the water was cold).
Please note that here "feel" is not used in the sense of "experience" as in the example of "He felt a sudden pain in his heart".
Here "feel" means "seem" or "give or produce a certain sensation" (感覺). When "feel" is used in this sense, the subject of "feel" is something that is described by an adjective or an adverb that follows "feel".
This shower feels great. 這淋浴的感覺好極了。
My feet feel cold. 我的腳摸上去很冷。
The clothes feel soft. 這衣服摸起來很柔軟。