Nothing puts the devils to flight like holy water

"I know by frequent experience that there is nothing which puts the devils to flight like holy water. They run away before the sign of the cross also, but they return immediately: great, then, must be the power of holy water. As for me, my soul is conscious of a special and most distinct consolation whenever I take it. Indeed, I feel almost always a certain refreshing, which I cannot describe, together with an inward joy, which comforts my whole soul. This is no fancy, nor a thing which has occurred once only; for it has happened very often, and I have watched it very carefully. I may compare what I feel with that which happens to a person in great heat, and very thirsty, drinking a cup of cold water -- his whole being is refreshed. I consider that everything ordained by the Church is very important; and I have a joy in reflecting that the words of the Church are so mighty, that they endow water with power, so that there shall be so great a difference between holy water and water that has never been blessed. Then, as my pains did not cease, I told them, if they would not laugh, I would ask for some holy water. They brought me some, and sprinkled me with it; but I was no better. I then threw some myself in the direction of the negro, when he fled in a moment. All my sufferings ceased, just as if some one had taken them from me with his hand; only I was wearied, as if I had been beaten with many blows. It was of great service to me to learn that if, by our Lord's permission, Satan can do so much evil to a soul and body not in his power, he can do much more when he has them in his possession. It gave me a renewed desire to be delivered from a fellowship so dangerous."

-- The Life of St Teresa of Avila by St Teresa of Avila
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Traditionally, in Carmel, usually on Sundays, a sister sprinkles all the rooms, offices and chapels in the monastery. Each cell (bedroom) also contains a vial of holy water so that each sister may sprinkle her cell and anoint herself when getting up in the morning, and in the evening before retiring. Consider keeping a bottle of this sacramental in your home and office, and anoint yourself while making the Sign of the Cross.

St Teresa had great confidence in the power of holy water to ward off evil. You may read more about St Teresa's experience with holy water on Chapter 31 of the book of her life (see column in the left for a link to a free online version).