The far-infrared absorption coefficient for absorption due to the presence of OH groups in amorphous silica has been investigated at room temperature, 200 K and 80 K, using a far-infrared laser. The observed absorption is interpreted in terms of an asymmetric double well, for which the theory has recently been derived by Hutt and Butcher (1988). This interpretation is discussed in relation to previously far-infrared, dielectric loss and heat capacity measurements.