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" (感觉). 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. 这淋浴的感觉好极了。
My feet feel cold. 我的脚摸上去很冷。
The clothes feel soft. 这衣服摸起来很柔软。