We have many water ways in our area. I think the sand on banks adjacent to active rivers has an incredible energy to it, a nice "charge." This sand feels both cleansing and energizing to me, and seems to have a "wisdom" to it, something ancient and grounding. I keep a good amount on hand, and use it for a number of things, including heat/fire related projects, spell work, you name it.
And it adds a nice energy to an altar just by itself, without "using" it for any particular thing. It feels alive to me, like an old friend. If you hold your hand over it, you can feel the kinetic action of the water that transported it. And you could feel the energy of the sun that irradiated it, as it may have been exposed to sunshine for many milennia (mind boggling to think about). I love river sand; I love the planet, my Mother.