Pura Luhur Batukaru is one of the kayangan jagat (directional temples), that protect Bali from evil spirits. Pura Luhur Batukaru protects Bali from the west. There are 9 kayangan jagat altogether and they are always temples that occupy auspicious locations, such as the sides of tall volcanoes or overlooking the ocean. Other kayangan jagat include Pura Besakih and Pura Luhur Uluwatu.
Pura Luhur Batukaru was originally built in the 11th century and was dedicated to the ancestors of the rajas of Tabanan. The temple was destroyed in 1604, but rebuilt in 1959. The most important shrine at Pura Luhur Batukaru is the 7-tiered meru that is in honor of the god of Gunung Batukaru, Mahadewa.
Galungan is the most important ceremony of the year in Bali and during that time people come from far and wide to pray. The holy waters of Pura Luhur Batukaru are used by members of the subak (water course governing body) for ceremonies to the Gods to ensure fertility of the land. If they pay their respects to the Gods controlling the water, they will always get water.
Quoted from : http://www.baliblog.com/travel-tips/bali-daily/pura-luhur-batukaru-a-bit-of-history.html