A devotional intention does not create an exception to transport rules. Keep containers securely closed and distinguish water for devotional use from other items in your luggage.
Lourdes · YOUR QUESTION, ANSWERED
Can I take Lourdes water home?
Yes. Lourdes spring water may be collected free at the taps near the Grotto, and pilgrims routinely carry it home. Airline liquid limits apply: containers in carry-on baggage are limited to 100 ml (3.4 oz) each, so checked baggage is the usual way to bring more. Use a suitable sealed container and collect only what you can responsibly carry.
Sources & further readingSanctuary of Lourdes: the waterTSA: liquids rule
Official sources cover institutional information. Suggested pacing and itinerary choices are planning guidance. Check current arrangements for your travel dates.