A comparison of international standards might help to develop guidelines for the reference area within each particular project. In many countries like USA and Spain only regional standards exist. A very limited number of European countries have guidelines or regulations on wastewater reclamation and reuse because first they usually do not need to reuse water and second their rivers have a sufficient dilution factor.

The US and Saudi Arabia have, in the context of their technical standards, set a number of individual limit values for microorganisms and chemicals. This type of differentiation was pioneered by California, which as early as 1918 undertook some initial efforts concerning the reuse of wastewater; and later, with the growth of technical potentials, the US further differentiated and tightened up these regulations, the final outcome being extremely low limit values (California State Water Code). These strict limit values have no grounds in medical science and take considerable effort to monitor and enforce. The 1989 WHO guidelines (see chapter 3.1) reflect this view.

Many developing countries focus on use restrictions in their legislation. Often, for example, such regulations ban wastewater irrigation for vegetables that can be eaten raw, or for edible plant parts in general, and require a minimum time interval between irrigation and crop harvest. The main problem with such use restrictions is that they cannot be monitored without functioning oversight agencies. The serious problems involved in monitoring use restrictions have led several countries, including Mexico (see chapter 3.4) and Tunisia (see chapter 4.1), to combine these two approaches: use restrictions plus easy-to-measure limit values for chemical and biological sum parameters (BOD₅ and COD) and micro-organisms, a practice that has given rise to a comprehensive and yet uncomplicated approach that, while doing justice to minimum safety needs, is still comprehensive enough to be generally conducive to the strategy of wastewater reuse.