I love it, however I have a problem because when I start pouring water my character falls over and starts sliding on the ground

That is no mod. This is a scenario. Find the scenario folder and open it and copy the hemmt init from the scenario...

The hemtt has no Init when I place it in the editor. Which in my view renders the mod completely useless?

I could copy your mission to my mission folder an open it. Also i could copy the init to a HEMMT in an other mission. Also in my mission i could take the hoste and let flow water.
Now i have 2 remarks: First, unfortunately i can not stop the water flow. Maybe your script in the vehicle init should also contain the possibility to stop the flow.
The other remark does not concern your work, but the fire module from the reaction force DLC. When i tested it in my mission my "firefighter" dies at the moment pulled water to the fire. Then i find out, that in your sample mission the damage is switched off in the init of the firefighter.
This is not ideal for mission makers, but maybe acceptable for exclusive fire fighting missions.
It will be great, when somebody knows how i can lower the damage from the fire to the man.
Maybe we could use following mod: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2645823531 .

Thank you!

So, there is supposed to be something like the internet where there are search engines which help you....
Google [www.google.de] is one of them.
Basically you find the file on your computer, paste it into your missions and then are able to open it.

How do i open the scenario you made in my editor?

Like I said in the description, you copy the init of hemtt and paste it into the init of the vehicle you want to use as the firefighting vehicle.
So you open the scenario in eden editor, double click on the hemtt, copy the init field. Exit the mission, open the mission where you want to use this, and paste it.

how do i make it work?