| Sg. Indef. | vatnskassi |
| Sg. Def. | vatnskassinn |
| Pl. Indef. | vatnskassar |
| Pl. Def. | vatnskassarnir |
| Sg. Indef. | vatnskassa |
| Sg. Def. | vatnskassans |
| Pl. Indef. | vatnskassa |
| Pl. Def. | vatnskassanna |
| Sg. Indef. | vatnskassa |
| Sg. Def. | vatnskassanum |
| Pl. Indef. | vatnskössum |
| Pl. Def. | vatnskössunum |
| Sg. Indef. | vatnskassa |
| Sg. Def. | vatnskassann |
| Pl. Indef. | vatnskassa |
| Pl. Def. | vatnskassana |