I recommend either a portable filer, iodine tablets. Bottled water is widely available in touristy areas but difficult to come by in the country areas. Food Food is good, though variety is limited. Fruit is not widely available except for bananas. Hygiene standards are sometimes questionable.
Water is always offered but avoid it - it's usually from a barrel rather than a hand pump.
Eat with right hand and wash hands before and after. Nepalis always do this and are quite hygienic that way. This may seem impossible in such a densely populated country setting up towards dusk is the trick. Nepalese consider it strange that a Westerner doesn't stay in hotels all the time. Simplest if you can too adapt to this also.