http://www.bukkit.fr/index.php/topic/13125-remplacer-seulement-leau-ou-la-lave-venant-de-la-source/

Fluids.java

package fr.neatmonster.fluids;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.player.PlayerInteractEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class Fluids extends JavaPlugin implements Listener {
    private static final List<BlockFace> FACES = Arrays.asList(BlockFace.DOWN, BlockFace.EAST, BlockFace.NORTH, BlockFace.SOUTH, BlockFace.WEST);
    private static final List<Material>  LAVA  = Arrays.asList(Material.STATIONARY_LAVA, Material.LAVA);
    private static final List<Material>  WATER = Arrays.asList(Material.STATIONARY_WATER, Material.WATER);

    private static void collectFluid(final Block anchor, final Map<Block, Material> collected, final List<Material> fluid) {
        if (fluid.contains(anchor.getType()) && !collected.keySet().contains(anchor)) {
            collected.put(anchor, anchor.getType());
            for (final BlockFace face : FACES)
                collectFluid(anchor.getRelative(face), collected, fluid);
        }
    }

    private static Material getOpposite(final Material fluid) {
        switch (fluid) {
        case LAVA:
            return Material.WATER;
        case STATIONARY_LAVA:
            return Material.STATIONARY_WATER;
        case STATIONARY_WATER:
            return Material.STATIONARY_LAVA;
        case WATER:
            return Material.LAVA;
        default:
            return Material.AIR;
        }
    }

    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler(ignoreCancelled = true)
    public void onPlayerInteract(final PlayerInteractEvent event) {
        if (event.getAction() == Action.RIGHT_CLICK_BLOCK && event.getMaterial() == Material.DAYLIGHT_DETECTOR) {
            final Block anchor = event.getClickedBlock().getRelative(event.getBlockFace());
            if (anchor.getType() == Material.STATIONARY_LAVA || anchor.getType() == Material.STATIONARY_WATER) {
                final Map<Block, Material> fluidBlocks = new HashMap<Block, Material>();
                collectFluid(anchor, fluidBlocks, anchor.getType() == Material.STATIONARY_LAVA ? LAVA : WATER);
                for (final Block fluidBlock : fluidBlocks.keySet())
                    fluidBlock.setType(Material.AIR);
                for (final Entry<Block, Material> fluidBlock : fluidBlocks.entrySet())
                    fluidBlock.getKey().setType(getOpposite(fluidBlock.getValue()));
                event.setCancelled(true);
            }
        }
    }
}

plugin.yml

name: Fluids
version: 1.0
author: NeatMonster
main: fr.neatmonster.fluids.Fluids