The height \( h \) of water in a capillary tube is determined by the capillary rise formula:
\[h = \frac{2T \cos \theta}{r \rho g},\]
where \( T \) denotes surface tension, \( \theta \) is the angle of contact, \( r \) is the tube radius, \( \rho \) is the liquid density, and \( g \) is the acceleration due to gravity.
The volume of water in the capillary is calculated as:
\[V = \pi r^2 h = \pi r^2 \cdot \frac{2T \cos \theta}{r \rho g}.\]
Upon simplification:
\[V \propto r.\]
The mass of water in the capillary is:
\[m = \rho V \propto r.\]
For a capillary with a radius of \( 2r \), the updated mass is:
\[m_2 = 2m_1,\]
indicating that the water mass is directly proportional to the capillary tube's radius.
Therefore, the new mass is:
\[2M.\]
Final Answer:
\[\boxed{2M}.\]