The ability you want in Pokemon Pokopia is a move literally called Suck, and it is not Water Gun. That confusion is why this search comes up empty so often. Water Gun only sprays water outward in a cross pattern to revive dry plants. Suck inhales liquid so you can move it somewhere else.
Two Ways to Unlock Suck
Befriend Paldean Wooper. Build a marshy tall grass habitat: four yellow tall grass tiles beside a body of muddy water. Note that sources disagree about where this is best done, some placing it at Bleak Beach and others during a Rocky Ridges request, but the habitat requirement itself is consistent.
Complete Piplup’s “Make a Waterfall” request. This becomes available after you rebuild the Rocky Ridges Pokemon Center. Importantly, you have to talk to Piplup directly to start it; it does not appear in your request list on its own, which is why plenty of players never find it.
Using It
The controls are hold Y plus ZR to inhale, A to spit it back out, and B to gulp and discard what you are carrying.
It works on more than you would expect: ordinary water, ocean water, hot spring water, vending machine drinks, and lava.
The Warning Worth Reading
Spitting liquid onto open terrain spreads messily and can flood nearby habitats. Treat Suck like a bucket in any sandbox builder: move liquid into enclosed basins you have prepared, not onto flat ground you like the look of.
Used deliberately, it is one of the most powerful terraforming tools you have. Creating and enlarging bodies of water is one of the main ways to raise an area’s humidity, which our humidity guide covers, and it lets you manufacture the waterside spot a Concrete Mixer needs rather than hunting for one.
Can You Upgrade It?
Water Gun can be upgraded. Suck apparently cannot.
Eating any soup powers up Water Gun so it waters more blocks when held, which is confirmed for Simple, Healthy, Flavorful, Electrifying, Mushroom and Seaweed Soup. Simple Soup is Fresh Water x1 plus any two Ingredients, cooked in a Cooking Pot on a stove or campfire, with cooking unlocking in Rocky Ridges.
No source we found describes an equivalent upgrade for Suck, so treat its capacity as fixed.
Frequently Asked Questions
Does Water Gun suck up water?
No. Water Gun sprays outward to water plants. Sucking water up is a separate move called Suck.
How do I get the Suck move?
Either befriend Paldean Wooper with a marshy tall grass habitat, or complete Piplup’s Make a Waterfall request after rebuilding the Rocky Ridges Pokemon Center.
What can I suck up?
Water, ocean water, hot spring water, vending machine drinks and lava.
Can I upgrade Suck?
Not that we could find. Soup upgrades Water Gun, but no equivalent exists for Suck.