護摩壇之造法。有地水火風四種。圓形者曰水壇。又小者為木壇。無論在何處，皆得自由持行，如水之流，故曰水壇。又急病兵亂等起時，在屋宅中作壇，唯以灑水淨之。故名水壇。
The water, or round, altar in the homa, or Fire ceremonial of the esoterics; also an altar in a house, which is cleansed with filtered water in times of peril.
一水壇 密教護摩壇之一種。密教之護摩法本須在七日之中擇地、擇時、掘地、治地，灑香水而加持之，然若於急病或兵亂等災變起時，僅須灑水淨地，於一日中即可建壇，稱為水壇；又以土築壇，故亦稱土壇。此外，木壇亦行灑水加持，且無場所限制，能自由持行，如水之流動自在，故亦稱水壇。p1952