Amor seco essence is healing water in the Dragon Quest series.
Amor seco essence can be purchased for 120 gold coins and sold for 90. Amor's item shop is the only place to buy it regularly. 3 of them can also be purchased with a Chimaera wing for 400 gold coins at Haggleton during it's second and final Bazaar.
It can also be found in Amor by searching some barrels and pots, as well as a chest in Murdaw's Keep. Some monsters will drop it after battle, including:
The essence can replenish the target's HP by about 60. The potency of the item is similar to that of Midheal.