I made home brew lager from bottled water. Can I use the plastic bottles to bottle up? or potential bomb?

Potential bomb I am afraid, we're not talking weapons of mass destruction here but possibly enough to splatter beer all over the cupboard, angry parent\partner potential is very high. Use proper beer bottles or invest in a barrel. I think if the bottles are from carbonated drinks such as fizzy water you may get away with it but it still has a risk (a friend of mine used them and occasionally he had a splatter fest)