First off you need to know the symptoms of low E2, they are typically mind fog, low sex drive, joint pains, water retention.
As far as I know, according to what I have read and my own experience, water retention is NOT a sign of low E2, but rather of high E2. Low sex drive and brain fog are also not reliable symptoms, as they can both be caused by low E2 and high E2.
Joint pain, on the other hand, is a reliable symptom of low E2. Think about it, water retention and joint pain don’t really go together, because one of the causes of joint pain is lack of fluid to cushion the joints.
I could be wrong, and am curious about others experience because E2 seems to be one of the trickiest things to figure out for trt, and something for which the symptoms of would be really worthwhile to have an accurate and reliable description.