Sounds like a good idea but what is a pet bottle?

I don't know what a pet bottle is either, but I'm thinking that it's a good idea and any kind of plastic soft drink bottle or water bottle might work.

I think the main problem would be to make the small hole the right size.

Down here, water would get very hot during a sunny day. I wonder if this would damage the plant as they seem to do better if the root system is cooler than the top.

Me, I use 5 liter plastic water bottles, punch holes in the wide area around the neck, upturn them and cut the 2-3 in. bottom (now the top) off, but not completely, so the "lid" can be opened and closed, usually held closed with a rock. I bury the bottle neck down about halfway or less, and fill it with water from hose or bucket. The plants are planted in a circle around each bottle. The water seeps through the holes directly to the roots - no evaporation, no waste.

Now that the full Middle East summer is gearing up, I have been filling these bottles - meaning I have been watering my garden - only once a week! As it gets really hot through to the end of august, I'll up that, but I can guarantee that I'll water less, waste less and pay less for water.
I have a bucket in the shower, which every day goes on another part of the upper container garden. For the lower veggie/herb/flower gardens, which all have the buried bottles, I'll be collecting the water that drips from the air conditioners and using that to fill the bottles.
With all of this, I barely open the hose, barely pay for city water, and so far the garden is happy.
I based all of this loosely on "buried clay pot" irrigation. I use one clay unglazed pot and it works just as well as the bottles. The tomatoes are so big now I have to push them aside to get to the bottle and they can barely be seen.
Want pics?
Peace

Yes, Batya, please send some pics! This is so interesting!
I always save leftover Coke and mix it in with water in the watering can
for an extra sugsr shot for the soil.