To provide a portable water mat which is portable and is comfortable to sit in and to sleep and provides comfortable temperature.

A plastic film is thermally adhered together with a cap and a heat retaining material is put therein and covered with a waterproof cover. Adjusted raw lime is filled into water in a commercially available PET bottle container and completely dispersed to obtain solution, which is poured from the cap of the water mat and the cap is closed after the solution is completely poured.