Question: what is the major cause of water scarcity in south africa
[{'answer': 'drought', 'provenance': [{'wikipedia_id': '54197701', 'title': 'Cape Town water crisis', 'start_paragraph_id': 10, 'start_character': 78, 'end_paragraph_id': 10, 'end_character': 85, 'bleu_score': 1.0, 'section': 'Section::::Timeline.:2015–2016.\n'}]}]