Complex sentence: Since the water was stored between uses in unlined ponds, it ultimately severely contaminated the groundwater in the town, which led to a legal battle that was the subject of "Erin Brockovich", a 2000 drama film.
Split into simpler sentences: Since the water was stored between uses in unlined ponds, it ultimately severely contaminated the groundwater in the town. The legal case was the subject of "Erin Brockovich", a 2000 drama film.