The Lympha (plural Lymphae) is an ancient Roman deity of fresh water. She is one of twelve agricultural deities listed by Varro as "leaders" (duces) of Roman farmers, because "without water all agriculture is dry and poor." The Lymphae are often connected to Fons, meaning "Source" or "Font," a god of fountains and wellheads. Lympha represents a "functional focus" of fresh water, according to Michael Lipka's conceptual approach to Roman deity, or more generally moisture.

Vitruvius preserves some of her associations in the section of his work On Architecture in which he describes how the design of a temple building (aedes) should reflect the nature of the deity to be housed therein:

The character of the Corinthian order seems more appropriate to Venus, Flora, Proserpina, and the Nymphs [Lymphae] of the Fountains; because its slenderness, elegance and richness, and its ornamental leaves surmounted by volutes, seem to bear an analogy to their dispositions.

The name Lympha is equivalent to, but not entirely interchangeable with nympha, "nymph." One dedication for restoring the water supply was made nymphis lymphisque augustis, "for the nymphs and august lymphae," distinguishing the two as does a passage from Augustine of Hippo. In poetic usage, lymphae as a common noun, plural or less often singular, can mean a source of fresh water, or simply "water"; compare her frequent companion Fons, whose name is a word for "fountain," but who is also invoked as a deity.

When she appears in a list of proper names for deities, Lympha is seen as an object of religious reverence embodying the divine aspect of water. Like several other nature deities who appear in both the singular and the plural (such as Faunus/fauni), she has both a unified and a multiple aspect. She was the appropriate deity to pray to for maintaining the water supply, in the way that Liber provided wine or Ceres bread.

The origin of the word lympha is obscure. It may originally have been lumpa or limpa, related to the adjective limpidus meaning "clear, transparent" especially applied to liquids. An intermediate form lumpha is also found. The spelling seems to have been influenced by the Greek word νύμφα nympha, as the upsilon (Υ,υ) and phi (Φ,φ) are normally transcribed into Latin as u or y and ph or f.

That Lympha is an Italic concept is indicated by the Oscan cognate diumpā- (recorded in the dative plural, diumpaís, "for the lymphae"), with a characteristic alternation of d for l. These goddesses appear on the Tabula Agnonensis as one of 17 Samnite deities, who include the equivalents of Flora, Proserpina, and possibly Venus (all categorized with the Lymphae by Vitruvius), as well as several of the gods on Varro's list of the 12 agricultural deities. On the Oscan tablet, they appear in a group of deities who provide moisture for crops. In the Etruscan-based cosmological schema of Martianus Capella, the Lymphae are placed in the second of 16 celestial regions, with Jupiter, Quirinus, Mars (these three constituting the Archaic Triad), the Military Lar, Juno, Fons, and the obscure Italo-Etruscan Novensiles. A 1st-century A.D. dedication was made to the Lymphae jointly with Diana.

The Italic lymphae were connected with healing cults. Juturna, who is usually called a "nymph," is identified by Varro as Lympha: "Juturna is the Lympha who aids: therefore many ailing people on account of her name customarily seek out this water", with a play on the name Iu-turna and the verb iuvare, "to help, aid." Juturna's water shrine was a spring-fed lacus in the forum which attracted cure-seekers, and Propertius connected its potency to Lake Albano and Lake Nemi, where the famous sanctuary of Diana Nemorensis was located. Juturna's cult, which Servius identifies as a fons, was maintained to ensure the water supply, and she was the mother of the deity Fons.