There are no "pools of water" inside or immediately near the Taj Mahal. The iconic water feature is a long rectangular reflecting pool (hauz) aligned on the north-south axis, extending from the main gateway to the mausoleum plinth.
The Taj complex sits on the south bank of the Yamuna River. The river itself is the primary water body—integral to Mughal garden design (charbagh) and structural foundation (ebony wells, sal wood beams require moisture).
Photos at dawn/dusk show mirror-like reflection in the pool—often mistaken for a "pool" in the sense of a swimming basin. The pool is shallow (~0.5 m), decorative, not for bathing.
Yamuna pollution and reduced flow threaten foundation stability. ASI monitors moisture levels; Yamuna Action Plan aims to restore flow/quality.