Pond
From PinataIsland.info, the Viva Piñata wiki
A pond is a body of water that is required to attract some Piñatas. To dig a pond you'll need a Pond Shovel Head upgrade that is awarded upon reaching level 7. Awarded at level 30 is the Platinum Shovel Handle which decreases the time it takes to dig a pond.
Piñatas that require a pond are:

 Appear Requirement 1 of 1 = Have 400 square pinometers of water (40%).
 Visit Requirement 1 of 2 = Have 500 square pinometers of water (50%).
 Resident Requirement 1 of 4 = Have 600 square pinometers of water (60%).
 Romance Requirement 1 of 5 = Have 700 square pinometers of water (70%).

 Resident Requirement 1 of 3  Have 160 pinometers of water (16%) .

 Visit Requirement 1 of 2 = Have 160 square pinometers of water (16%).
 Resident Requirement 1 of 2 = Have 190 square pinometers of water (19%).
 Romance Requirement 1 of 4 = Have 220 square pinometers of water (22%).

 Visit Requirement 1 of 1 = Have 150 square pinometers of water (15%).
 Resident Requirement 1 of 3 = Have 200 square pinometers of water (20%).
 Romance Requirement 1 of 5 = Have 250 square pinometers of water (25%).

 Romance Requirement 1 of 4 = Have 100 square pinometers of water (10%).

 Romance Requirement 1 of 4 = Have 60 square pinometers of water (6%).

 Visit Requirement 1 of 1 = Have 10 square pinometers of water (1%).
 Resident Requirement 1 of 2 = Have 20 square pinometers of water (2%).

 Appear Requirement 1 of 1 = Have 20 square pinometers of water (2%).
 Visit Requirement 1 of 2 = Have 30 square pinometers of water (3%).
 Resident Requirement 1 of 2 = Have 30 square pinometers of water (3%).
 Romance Requirement 1 of 3 = Have 30 square pinometers of water (3%).

 Appear Requirement 1 of 1 = Have 30 square pinometers of water (3%).
 Visit Requirement 1 of 2 = Have 40 square pinometers of water (4%).
 Resident Requirement 1 of 2 = Have 40 square pinometers of water (4%).

 Visit Requirement 1 of 2 = Have 250 square pinometers of water (25%).
 Resident Requirement 1 of 2 = Have 250 square pinometers of water (25%).
 Romance Requirement 1 of 5 = Have 300 square pinometers of water (30%).

 Visit Requirement 1 of 2 = Have 120 square pinometers of water (12%).
 Resident Requirement 1 of 3 = Have 140 square pinometers of water (14%).
 Romance Requirement 1 of 3 = Have 140 square pinometers of water (14%).
Pond Strategies
 Pinatas become slightly happier when they drink from a pond.
 You can get an almostexact amount of pond if you use fence as your pond's boundary. The border of the pond will not go past the fence.
 The best fence to use for this is the Wire Fence.