Recent studies of the non-linear response of the conventional tide-well system have pointed out the deficiencies of the system when the tide records are to be used for scientific purposes requiring very accurate data. An experimental method of checking the response of such tidewells, by means of a drainage test, is described. This provides the basis of a further method, by which the height of the water level in the well may be approximately corrected to give the height of the sea level outside the well. The application of these methods, to a recently advocated linear tide-well system, is also described.