Tank.  Pond.  Taalaab. Tadaag is a reservoir over 2,000 square cubits in area and not less than 45 cubits in width. Other kinds of tanks are

(1) Drone (40 x 40 cubits and over);
(2) Vaapi (130 x 130 cubits and over);
(3) Sarovar is large tank where the lotus grow;
(4) Deerghikaa should be 35 cubits wide with a superficial area of not less than 1,200 square cubits;
(5) Pushkarinee in not less than 20 x 20 cubits;
(6) Koop is a well;
(7) Saagar is one that is larger than any one of the above.

These reservoirs, maybe except well, as it is normally round; should be long in shape from North to South, even those which are of a square shape should be slightly longer from North to South. When a tank is first dug out, a thick column or piece of wood is driven into its center (it is called Naag Stambh or Yoop) and some aquatic animals (artificial frogs or fish etc) should also be placed in the tank. There should be made two fish and two frogs of gold, two alligators of silver, and two tortoises - one of copper and another of brass.

After placing these animals in the Tadaag, Naag should be supplicated and worshipped. Anant, Vaasuki, Padm, Mahaapadm, Takshak, Kulir, Karkat, and Shankh - all these are the protectors of water. These eight names of the Naag should be written on Ashwatth (banyan tree) leaves and after making Jap of the "Aum" and the Gaayatree, the leaf should be thrown into a jar. Calling upon Sun and Moon to witness, the leaves should be mixed up together, and one half should be drawn there from and the Naag whose names are drawn should be made the protector of the water. They should be worshipped.
[Mahaa Nirvaan Tantra, p 314-315]