If quartz sand releases silicates into water, all water on the planet would have lots of silicates in it. Quartz doesn't dissolve at all in water. Quartz is a crystal form of silicate, while glass is a non-crystal form, and also doesn't dissolve in water. If it did, any glass object kept wet would become somewhat frosted, and that doesn't happen. Water soluble silicate is sodium silicate - water glass - a different compound.