A water tank is 3 m long, 2 m broad and 1 m deep.

Length of the water $\operatorname{tank}=3 \mathrm{~m}$

Breadth $=2 \mathrm{~m}$

Height $=1 \mathrm{~m}$

Volume of the water $\operatorname{tank}=3 \times 2 \times 1=6 \mathrm{~m}^{3}$

We $\mathrm{know}$ that $1 \mathrm{~m}^{3}=1000 \mathrm{~L}$

i.e., $6 \mathrm{~m}^{3}=6 \times 1000 \mathrm{~L}=6000 \mathrm{~L}$

$\therefore$ The water tank can hold $6000 \mathrm{~L}$ of water in it.