Quantitative measurements to detect lymphedema early in persons at-risk for breast cancer (BC) treatment-related lymphedema (BCRL) can aid clinical evaluations. Since BCRL may be initially manifest in skin and subcutis, the earliest changes might best be detected via local tissue water (LTW) measurements that are specifically sensitive to such changes. Tissue dielectric constant (TDC) measurements, which are sensitive to skin-to-fat tissue water, may be useful for this purpose. TDC differences between lymphedematous and non-lymphedematous tissue has not been fully characterized. Thus we measured TDC values (2.5 mm depth) in forearms of three groups of women (N = 80/group): 1) healthy with no BC (NOBC), 2) with BC but prior to surgery, and 3) with unilateral lymphedema (LE). TDC values for all arms except LE affected arms were not significantly different ranging between 24.8 ± 3.3 to 26.8 ± 4.9 and were significantly less (p < 0.001) as compared to 42.9 ± 8.2 for LE affected arms. Arm TDC ratios, dominant/non-dominant for NOBC, were 1.001 ± 0.050 and at-risk/ contralateral for BC were 0.998 ± 0.082 with both significantly less (p < 0.001) than LE group affected/control arm ratios (1.663 ± 0.321). These results show that BC per se does not significantly change arm LTW and that the presence of BCRL does not significantly change LTW of non-affected arms. Further, based on 3 standard deviations of measured arm ratios, our data demonstrates that an at-risk arm/contralateral arm TDC ratio of 1.2 and above could be a possible threshold to detect pre-clinical lymphedema. Further prospective measurement trial are needed to confirm this value.