Water rockets are very fun but if used incorrectly the can be extremly dangours...
Even on the launch pad.
Step 1: Pressure test the make of your bottles
it didn't turn out well.
most fizzy drink bottles should not lose and shape and pressure to 140 PSI
I would not by cheap ones but mabye well known brands as they are better.
Its better to be safe than stupid.
When initially pressure testing the rocket, fill it with water. If it explodes it will be less catastrophic.
Step 2: Make rockets with care and time
If you rush though you design you increase you risk of an explosion
Step 3: Have safty rules when launching rockets
All uneeded personell must stand 5 meters away from the rocket
Personell needed to launch must wear eye protection
If a rocket is falling near you walk away. DO NOT RUN!
Never touch the rocket when pressurized
Check the is no personel down range when launching
Never pressurize a rocket with someone in its immediate vacinity.
Never check a loaded rocket, with your head above it. Chances are it will go off when you are checking it.
Never unless there is no other option, approach a loaded rocket.
Step 4: Safty rules about and when making rockets
Use only glues suitable for joining bottle plastics. This glue also needs to be pressure rated, not just able to glue plastic.
Do not continue using the same rocket for many months on end. Your joints/bottles receive fractures from impact, the plastic also deteriorates ending in blow outs.
Step 5: Safty about the launching area
Check surrounding area before launching, if wind picks up at height, i've had rockets drift hundreds of metres on the wind, ending up no-where near where I had expected.
Never leave rocket in the sun for extended period of time. The bottles warp, the plastic become unstable.
By Oscar Thompson
with thanks to instructable member: Lftndbt