You can’t go far wrong using a Buytl lining… you are better buying a quality liner with a good guarantee than scrimping on a cheaper material only to get a puncture or punctures … once everything is in place , you don’t want to start again been there , many years ago & never again .
The thicker grade Butyl is very robust and should take your water feature ok as long as you install the feature etc with respect to the liner .
Make sure you check the prepared site for flints , sharps etc and then place old carpet or carpet underlay on the “ hole etc to be a protective cushion layer under the liner .
This was a tip I was given by a professional installer to help prevent any overlooked sharps getting through.
Good luck , you will be amazed how much soil etc comes out of a small hole !!
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