How to use it follows the words Bernadette heard at the ninth apparition: go and drink at the spring and wash yourself there. Pilgrims drink from the fountains, wash their face and hands, and fill bottles to carry home; the water gesture at the baths, led by volunteers, does the same three things in a prayerful setting. Bernadette's own comment, quoted by the Sanctuary, sets the tone: the water is taken like medicine, but faith and prayer are needed, because the water has no virtue without faith.
Is it holy water? No. Holy water is water a priest has blessed for liturgical use. Lourdes water is unblessed spring water that pilgrims value because of what happened at the Grotto, and a bottle brought home can be used for drinking, for washing a sick person's forehead, or as a reminder to pray; some families ask their parish priest to bless it, which is a separate act. The Sanctuary's position on healing is on the existing page about whether Lourdes water guarantees healing.
Where to get it: at the Sanctuary, bring your own container or buy one in the town's shops, then fill it at the taps, which are free. The Sanctuary does not ship water to individuals; its page says people who cannot travel should contact the pilgrimage organization nearest them, which in the United States means a diocesan or national Lourdes pilgrimage. Water sold online is not endorsed by the shrine. Taking it home is covered on the existing page about bringing Lourdes water home.