In Morrisons, if you buy a bottle of their Value range sparkling (10p) or still (13p) water, you receive a free box of "Wahoo"
From the Wahoo website:
"Wahoo flavourbursts, developed by the hydration experts at Santeau, have a great taste, low calories and provide the added benefit of easier portability so people can turn plain water into Wahoo - anytime anywhere with anywater!
The new Wahoo's fit easily into a handbag or gym bag for ultimate convenience.
Now available in three fantastic and refreshing flavour combinations: Summer Berry, Tropical Fruits and Citrus Twist.
To enjoy; open a sachet, pour Wahoo into a 500ml bottle of water, shake to activate and enjoy the great taste and hydration benefits.
Wahoo is a lightly flavored low calorie vitamin-enhanced drink mix which hydrates and nourishes the active body during workouts and throughout the day with only 10 calories per 500ml serving,
Wahoo is a great alternative to plain water because its light flavor helps active people drink more and stay hydrated. "
More info: http://www.wahoolife.com/
It's quite good actually, and since it's free, then you're not exactly wasting anything if you don't like it..
Doesn't seem to be a maximum purchase either,