The word translated "water in Neh 4:23 is simply מַיִם (mah'-yim) and simply means "water".
However, it is obvious that more than just water is intended. The Hebrew is obscure because the literal rendering is "each one his weapon the water", which makes no sense.
Therefore, most version supply another verb. There are several possible understandings here:
- Water could mean "water of the feet" that is urine. Such a meaning is found elsewhere according to BDB. 2 Kings 18:27 = Isaiah 36:12; compare מַדְמֵנָה בְּמֵי Isaiah 25:10 Kt in water of a dunghill.
- Some versions suggest that the "water" here is "washing", and that appears possible, eg, KJV, NKJV, HCSB, DRB.
- Water could also mean simply "water", ie, when each man went for a drink or refilled his water bottle. I think this last meaning is unlikely as such a meaning would not normally require the removal of clothes.
Therefore, I think it simplest to understand this reference to water as ablutions generally, that is, either washing or toilet as both involved water.