Bring the water to a boil in a medium saucepan. Add the limes, valerian root, borage and sugar. Bring back to a boil. Cover and simmer for 20 minutes over low heat. Keep warm over very low heat.
Before serving, pour a glassful of tea and return it to the saucepan to make sure the tea is evenly mixed.
Fill each glass with tea and adjust to taste by add