pocketmine\block\Block::canBeFlowedInto PHP Method

    public function canBeFlowedInto()
    {
        return false;
    }

 private function flowIntoBlock(Block $block, $newFlowDecay)
 {
     //So this the actual block setting
     if ($block->canBeFlowedInto()) {
         if ($block->getId() > 0) {
             $this->getLevel()->useBreakOn($block);
         }
         $this->getLevel()->setBlock($block, Block::get($this->getId(), $newFlowDecay), true);
         //if($newFlowDecay >= 0){ //This should actually be added somewhere else, now no water will go away
         $this->getLevel()->scheduleUpdate($block, $this->tickRate());
         //}
     }
 }