I read about Twestival in the Irish Times, of all places. Through the main festival page you can buy music or buy a t-shirt – presumably the proceeds go to the charity.
Who they are From Charity: water website charity: water is a non profit organization bringing clean, safe drinking water to people in developing nations. We give 100% of the money raised to direct project costs, funding sustainable clean water solutions in areas of greatest need. Just $20 can give one person in a developing nation clean water for 20 years.