If you try this at home, here are a few tips...
1. Don't just guess your weight is heavy enough to hold down the bottle. Test it first.
2. Dry ice filled water bottles will explode fast...like less than 10 seconds fast.
3. Liquified gasses will take longer to explode, around 3 minutes. never never never approach a bottle under pressure. get a bb-gun, or a long stick with a nail on the end to detonate it if you have problems.
4. Don't do this above ground if you want to stay friends with your neighbors. Above ground it will sound like a bomb just went off.