Help sealing granite stream

Hi Folks

I have a stream that worked well many years ago it made from granite
stone and is approx 5 inches wide and 2 inches deep. The base and
sides are made from granite and are set on a concrete base with a
liner under the granite sets to stop leakages. Over the years cracks
have appeared in the cement joints which I can easily fix but what I
wanting advice on is a way to cut down on evaporation and leaks. The
granite absorbs heat and water so it quickly evaporates water.

What I thought was maybe using some aquatic silicone sealer to thinly
cover the granite any thoughts on this?

I have used G4 sealer but this discolours the granite so instead of
been a silvery grey colour it turns an offish grey/brown and looks
dirty.

Hope this makes sense.

Nelly