Colloidal nanoparticles have found many applications in various areas as bio-sensing, bio-medicine, catalysis, optics and photonics, new energy sources, cosmetics, etc. Laser systems provide unique possibilities not only for synthesis of these nanoparticles, but also for a control over their sizes. In fact, depending on the experimental conditions, laser interactions with colloidal nanoparticles can either promote nanoparticle growth or induce their fragmentation. Because of the complexity of the physical and chemical processes involved, many of these interesting effects are still unclear and require much more analysis. To better understand these processes, we numerically examine laser interactions with nanoparticles in the presence of a liquid environment. In particular, we focus attention at such effects as (i) laser field propagation, scattering and absorption; (ii) local field enhancement and liquid ionization; (iii) nanoparticle heating and fragmentation; (iv) final aggregation. The effects of laser wavelength and pulse duration, liquid environment, as well as of nanoparticle material, initial particle sizes and concentration are underlined based on the proposed combined modeling.