Over the past decade, the rapid development of nanotechnology from academic exploration to practical application have fueled extensive interests in utilizing nanomaterials in membrane fabrication and modification, creating novel “nanocomposite membranes”. This new paradigm of membrane design revolutionize the traditional membrane fabrication technique allowing people to create membranes with unique mechanical, physical, chemical and/or biological properties. The present study explores the fabrication, characterization, and utilization of two types of nanocomposite membranes in two water treatment applications. Novel nanocomposite nanofiltration membranes were fabricated by modifying commercial membrane with Ag-zeolite for long term control of membrane biofouling, a serious issue plaguing almost every membrane water treatment systems. The modified membrane, through sustained release of Ag, exhibited prolonged antimicrobial activity effective in prohibiting the attachment and fouling by bacteria cells. Once depleted of silver, the membrane can be easily regenerated, thus having the potential for addressing long term biofouling problem. The interplays among solution conditions (e.g., Cl- and cysteine), chemical state of loaded Ag (Ag+ or Ag(0)), and Ag-zeolite loading on membrane were elucidated. Under low ionic strength condition (low Cl- concentration), release of Ag was solubility limited and thus Ag+-zeolite and Ag(0)-zeolite had similar longevity, and high Ag-zeolite loading could prolong the antimicrobial efficacy. High ionic strength condition (high Cl- concentration), on the other hand, leads to significantly increased Ag release, and similar release kinetics between the high and low Ag-zeolite loading samples. Ag(0)-zeolite effectively stabilized the release of Ag and leads to prolonged antimicrobial efficacy. Effect of cysteine in low ionic strength condition was also investigated. High cysteine condition could significantly increase Ag leaching and reduce antimicrobial efficacy. But with low and environmentally-relevant cysteine concentration, the modified membrane still exert sustained antimicrobial activity, with the high Ag-zeolite loading samples exhibiting over 80% surface bacteria inactivation after 15 days. Another type of photothermal nanocomposite membranes were fabricated by modification of hydrophobic polymeric PVDF membranes with photothermal nanomaterials for membrane distillation. The modified membrane can effectively transfer light energy into heat in the close proximity to the membrane surface, thus accelerating the vapor generation efficiency for water production. Results show that the employed physical/chemical binding methods (solvent drop-casting and polydopamine binding) effectively created even layer of nanoparticle coatings with varied surface loading amount. It was also revealed that coating density was crucial in achieving satisfactory photothermal efficiency. The design addresses the inefficiency in energy utilization in current membrane distillation systems, and have great potential to help provide clean water provision in areas where energy and transportation is lacking.