I can't answer the question about malt. However, drinking plenty of plain water flushes out the kidneys, which is always a good idea. As diabetics we are advised to drink plenty of water throughout the day with small quantities at a time rather than a lot all at one go. Too much all at once can put strain on kidneys. I don't have any kidney damage but I do drink about 2 litres a day and that is without strenuous exercise. I include tea in that 2 litres.