Advice please ménage surface

[Chico]

A livery yard I ride at has a wonderful 60x40 outdoor school which has been totally unusable this year.
it has brilliant drainage and sits on top of a hill but is totally exposed to the elements.
it is silica sand with poly fibre and due to our very dry summer is just too dry and rides too deep.
even with constant watering it just dries out its like a desert!
any ideas what can be added to the sand to help keep the moisture in so we can ride it anyone had a similar experience and how did you rectify it.

 

[Magicmillbrook]

Is it the right type of sand? I had an arena that had builders sand with sort of felt strips (bit like clopf) that stopped it riding so deep, I didn't build it I hasten to add. My arena that I had built is sub angular sand and rubber chips and hasnt been watered all summer and is great