Since Waterwalking doesn't work on ARAM and Riot has been doing some ARAM rebalance work lately, I thought I could suggest a replacement rune for the map:
> Gain 20% Movement Speed for 1 second and an adaptive bonus of up to 18 Attack Damage or 30 Ability Power (based on level) for 6 seconds after being healed by a health shrine that an enemy took or that is on the enemy side of the map.
This includes both taking the shrine and being healed by the redemption effect, so you can get a refresh on the duration and the movement speed twice by taking both the shrine and staying long enough for the effect, or you can get it from your own shrines if an enemy took them. It gives a third option next to poke (Scorch) and scaling (Gathering Storm) in the form of rewarding aggressive play during windows of power, possibly for melee champions. The movement speed is a nice alternative to consider in comparison to the other two rune's flat damage increases.
Alternative rewards or adjusting the values could be considered.
The lore behind it would either be A) on the Howling Abyss that the Iceborn turned the power they had been given against the Watchers to liberate themselves, or B) on Butcher's Bridge that pirates like to 'liberate' things from their enemies.