Minecraft How to make poisonous water

Hello, this is how to make poisonous water in minecraft. This uses commands and must be used in creative mode. So first, get a very fast clock. Here's a video on how to make the fastest one (and recommended one):

Now once you have that clock, place a command block near the redstone block that is constantly being broken and replaced. In their, copy this and paste into the command block (ctrl+v)
/execute @a ~ ~ ~ detect ~ ~ ~ minecraft:water -1 /effect @p minecraft:instant_damage. That basically kills them in the water. If you want to make it actual poison other than damage, type minecraft: poison instead of the instant_damage. Even more, if you want to take it further, remove the entire part that starts at /effect. Replace it with /tp @p (coordinates) It will teleport them to the coordinates listed if they touch water. This can also be used in parkours, like the one on this server. Thank you!

Spoiler: Tips and Help

If you watched the video and are still looking for the command,
type /setblock ~0 ~1 ~0 minecraft:redstone_block 0 destroy
For commands to help the lag and spam from the clock, do
/gamerule doTileDrops false, and
/gamerule commandBlockOutput false.

I did not create this clock or invent the water command that detects players.
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