Waterproof

First you need to cove out the base of the walls.

To my knowledge, Drylok is not warrantied for horizontal surfaces or for water contact conditions. Check with their technical people before you use it, since it will be almost impossible to do anything else once it is applied.

I would simply use pool plaster anyway.

question is how long do you want it to last and what color does it need to be?

UGL Drylock looks like paint to me. for a fountain you need to use either a deck coating NeoGuard or Sonoguard that should last a little while may leak a little bit. If you want it to really last try CIM 1000, its considered a liquid aplied membrane. Its expensive but if you want to do it right this is probaly the only way to go. If you do go this route make sure whoever you buy it from explains how to use the product, you have to work fast when u mix the buckets it sets up in a matter of 20 mins.

But do not use that drylock... anything that is latex based and offers more then a 5 year warranty is garbage...