It is shown that the ultrasound acting on water under ambient conditions causes an increase in the longitudinal spin relaxation time T1 of the 1H nuclei measured by means of nuclear spin echo method at low levels of ultrasound irradiation when the cavitation effects can be neglected. This effect is due to ultrasonic heating of the water and, as a consequence, to the increase in the relaxation time T1 with increasing temperature. In the absence of cavitation effects, at low doses of ultrasonic irradiation, the relaxation time T1 in the distillated water increases linearly with increasing ultrasound power. In the case of tap water there is a supplementary increase in T1 with an increasing in ultrasound power P from P = 0 to P = 3.5 W caused by the removal of adsorbed paramagnetic oxygen molecules from water due to ultrasonic heating. It is given a theoretical interpretation of the observed linear increase in T1 under increasing in P.