Dispersion of nanocarbon materials in liquid media, via solution processing such as spraying, printing, spinning, etc. is one of the prerequisites for practical applications. Here we report that water-dispersible single-walled carbon nanotubes (SWCNTs) were prepared through successive treatments with chlorosulfuric acid (CSA)/H2O2 and N-methylmorpholine N-oxide (NMO) monohydrate. The powder of the CSA/H2O2- and NMO-treated SWCNTs (N-SWCNTs) could be readily redispersed in water in concentrations as high as 1 g l-1 without requiring a dispersant. The mechanism responsible for the high dispersity of the N-SWCNT powder in polar solvents, including water, was elucidated based on the high polarity of the NMO molecule. In order to highlight the wide applicability of the N-SWCNTs, they were used successfully to prepare conducting thin films by spray-coating plastic substrates with an aqueous hybrid solution containing the N-SWCNTs and Ag nanowires (NWs). In addition, a flexible, large-area thin-film heater was prepared based on the N-SWCNT/AgNW hybrid film with a transmittance of 93% and sheet resistance of 30 Ω sq-1.