Solution

Homogeneous mixtures are those in which the substances are in uniform composition and have a single phase.
(A) Distilled water $$\rightarrow$$ Pure substance
(B) Tap water $$\rightarrow$$ Contains some minerals and impurities which are uniform throughout. so it is a homogeneous mixture.
(C) Sand and water $$\rightarrow$$ Heterogeneous mixture
(D) Sawdust and water $$\rightarrow$$ Heterogeneous mixture
Hence, option B is correct.