Si Collection, Upper Volume
Radical: Water (shuǐ)
Entry: 沗
Kangxi stroke count: 8
Page 611, Entry 19
Collection of Characters (Zihui) states that this is the character for to add. It is different from the character for humble (tiǎn). The character for to add, 沗, is formed with the water radical, whereas the character for humble, tiǎn, is formed with the heart radical.
For reference: Ocean Compilation (Haipian) gives the pronunciation as pāng. The character 沗 is written with water at the bottom, which is distinct from the other form of the character 沗.
Si Collection, Upper Volume: 沗 is the character for to add.