2. Materials and methods
2.1. Collection of water samples in urban and rural environments
Samples from water tanks of urban compounds were collected between the months of February and April 2014. Our sampling scheme was designed so as to include representative drinking water samples from all major urban cities in Qatar. Seven of the water samples were collected from compounds in the greater Doha area: 1 from Simaisma and 1 from Al Khor located North of Doha, and 1 from Al Wakra, located South of Doha (Fig. 1). Participants were given nitrile gloves, a one-liter sterilized glass bottle and written instructions indicating how to sample water tanks aseptically. Water samples were stored in the dark covered with tin foil to prevent post sampling growth of photosynthetic cyanobacteria.