Rather than go into too much detail regarding hot vrs. cold water mix/strain/preparation, I could quote World health Organization and NIH or the discussions and comments when writing the
Codex(1) Standards for kava. But a summary editorial in Journal of the American Medical Association in 2010- "...the traditional kava beverage is prepared by cold water extraction of its roots. Historic use shows that kava is safe under the strict control of the rituals of Pacific cultures. The traditional beverage is consumed on a daily basis without apparent adverse effects,...". Historic use is a phrase used in reference to "Noble Kavas" and preparation method all points to potable water from the tap.
(1) The Codex Alimentarius is a collection of international food standards,
codes of practice, guidelines, and recommendations developed by the Codex Alimentarius Commission (CAC) to protect the consumers' health and ensure fair practices in the food trade. The CAC was established by the
Food and Agriculture Organization (FAO) of the United Nations and the
World Health Organization (WHO) in 1963, and today, it has more than 180 member countries and more than 200 intergovernmental and international
nongovernmental organizations as observers. The Codex Alimentarius has become the global reference point for consumers, food producers, national food control agencies, and the international food trade.