One should always have at home enough Theophany water to last the whole year, and make use of it at every need: in cases of illness, leaving on a journey, whenever one is upset, students prior to examinations, etc. People who drink a little Holy Water daily, before eating any kind of food, do well. It strengthens the powers of our soul - if it is done with prayer and reverence, and one does not merely expect a mechanical result from it.
The most important thing during illness is to offer to God patience and thanksgiving for His merciful visitations. Sickness purifies sins and gives one time to meditate on the past.