Physical, environmental and psychological stressors can lead to chronic diseases. Changes in physiological parameters during stress can be evaluated using heart rate variability (HRV). A study is conducted with one participant on a daily basis over six months. Bathtub ECG is measured during his daily bathing and used for HRV analysis. The HRV stress index (SI) is proposed to quantity the stress in the study. SI is computed and found to be significantly higher in either mental stress or physiological stress. The variations of SI show in high accordance with the work schedules of the participant.