Rawadanau, located in Serang, Banten, is the main water supply for the
Cilegon industrial area, West Coast of Java, Indonesia, has geothermal
potential. Understanding groundwater origin and quality is an essential
factor in determining appropriate actions to save water supply sources.
This paper aims to answer the groundwater origin that fills the
Rawadanau, whose rocks are composed of volcanic products with evidence
of the main elements of water chemistry and stable isotopes (δ2H and
δ18O). Analysis of pH, temperature, EC, HCO3ˉ is carried out in the
field, while other chemical elements and stable isotopes are analyzed in
the laboratory. Groundwater found consists of hot springs, cold springs,
dug wells, river water. Hierarchical analysis clusters based on water
chemistry and stable isotopes can be grouped into two, cluster K (K1 and
K2) and clusters L, respectively. Data of δ2H and δ18O of the spring
waters in the Rawadanau indicate that they are of meteoric origin, and
there has been evaporation from several springs. Water comes from
meteoric water with stable isotopes content of δ18O between -6.39 to
-4.82 ‰ and δ2H between - 41.35 to -31.30 ‰, which has been controlled
by two main mechanisms, namely rock dominance, and evaporation
dominance. Aquifers are composed of product volcanic with the dominant
composition rock of porphyritic andesite, basaltic andesite, and
andesite. The multivariate statistical analysis results besides pH and
SO4, all parameters (cation and anions) showed significant correlation.
There are four groundwater facies, namely Ca-HCO3, Ca-Mg-HCO3,
Mg-Ca-HCO3, and Na-Cl.