This is an interesting question that perhaps we should do a lot more research to answer.
Normally we choose water which Na and SO4 contents are as low as possible, ideally below 10mg/l; all the other metals less than 20 or about. However, I can say for now that if the metals have to be scientifically optimised with corresponding datas for each tea, no two Wuyi or Phoenix oolongs would have the same requirements. That is because the salt contents interact not only with various catechins, but also with the innate mineral contents in a tea. Since no two selections even under the same tea name variety would have the same amounts of these two sets of variables, each tea selection is bound to require a different “ideal” water for its best taste.
In practice, I think it is best to maintain the constant in the water variables so as to judge the ever so huge variations in tea substances in different tea selections. That generally applies to all teas.
