To provide a water-absorbing sheet having good performance such as quick water absorption on contact with water and little in falling off of adhered water-absorbing resin powder at handling of the sheet.

This binder is for adhering a water-absorbing resin powder to a water-permeable sheet-like base member, which is liquid at the time of having brought into contact with the sheet-like base member and the water- absorbing resin powder, and is cured by active energy rays and/or heat to make a water-absorbing sheet.