Healing Water is a liquid that gives Regeneration buff (restoring health over time) to whoever swims in it. It exists on Eden and Desert planets as lakes/puddles. It can also be found at the core of some (but not all) Gas Giant planets in infinite quantities.
It is extremely efficient as a liquid for Trays, because it multiplies the growth speed of plants by 1.225 (being second only to Organic Soup), and also gets consumed in 6 times lower amounts than regular Water.