By ponding up groundwater and slowing down lateral movement, retention can create or enlarge such saturated zones. These nuances must be appreciated in order to avoid the assumption that because a basin is a hydrological unit all water related processes in the basin are one and the same.
===Benefits and disadvantages of reusing wastewater for agriculture===
[[Image:water reuse2.jpg|thumb|right|200px|Source: [avani-kumaon.org avani-kumaon.org]]]
There are both positive and negative implications of wastewater reuse. The positive implications include: employment generation, food security for urban and peri-urban poor farmers, reliable supply of irrigation water and the recycling of nutrients in wastewater. Since wastewater is available all year round, the urban poor farmers and migrant laborers are assured of employment throughout the year. In the peri-urban areas along Musi, Hyderabad, it was found that wastewater-irrigated paddy contributes almost 43% of household food consumption. The high nutrient content of the wastewater helps farmers save on the fertilizer costs and its reliable supply helps increase the cropping intensity. Wastewater can also have a positive or negative impact on the property values. In Haroonabad, in Pakistan, the wastewater-irrigated land has a higher value than the canal-irrigated land.
[[Image:water reuse3.png|thumb|right|200px|Source: [http://apgreenjobs.ilo.org/resources/urban-wastewater-and-agricultural-reuse Asian Pacific Green Jobs Network]]]
On the other hand, because of the partial or no treatment of wastewater, it endangers the very livelihoods it generates over the long term. Long-term use of wastewater for irrigation increases soil salinity, accumulation of heavy metals in the soil, and finally breakdown of the soil structure.
This in turn leads to restriction on crop choice and reduction in yields over the long run. Along the Musi River near Hyderabad, where wastewater is drawn from the river for irrigation, the paddy (rice) production has reduced by 40-50%. Ample evidences are available which show that the
groundwater in all wastewater irrigated areas has high salt levels and is unfit for drinking. Further, high groundwater tables and waterlogging are also common features of these areas. Wastewater contains a number of pathogens of which human parasites such as protozoa and helminth eggs are of special significance which can cause diseases in user communities and consumers. Further, wastewater containing a high level of nutrients may cause eutrophication and cause imbalances in the ecology of the water bodies, it is released into.
===Reuse around the world===
===Water reuse links===
* [http://www.iwmi.cgiar.org/Publications/Working_Papers/working/WOR128.pdf Wastewater Reuse and Recycling Systems: A Perspective into India and Australia]. Gayathri Devi Mekala, Brian Davidson, Madar Samad and Anne-Maree Boland.
* [http://www.gwp.org/en/gwp-in-action/Mediterranean/News-and-Activities-GWP-Mediterranean/Non-Conventional-Techniques-for-Water-Reuse-in-the-Mediterranean/ Non-Conventional Techniques for Water Reuse in the Mediterranean]
* [http://www.limpoporak.com/en/management/water+demand/conservation+and+reuse.aspx Limpopo river awareness kit: Conservation and reuse].
* [http://bebuffered.com/downloads/3R_managing_the_water_buffer_2010.pdf Managing the Water Buffer for Development and Climate Change Adaptation: Groundwater Recharge, Retention, Reuse and Rainwater Storage], Frank van Steenbergen and Albert Tuinhof.
* [http://www.watereuse.org/files/images/04-007-01.pdf Status and Role of Water Reuse], Global Water Research Coalition.
* [http://www.iwmi.cgiar.org/Publications/Working_Papers/working/WOR128.pdf Wastewater Reuse and Recycling Systems: A Perspective into India and Australia]. Gayathri Devi Mekala, Brian Davidson, Madar Samad and Anne-Maree Boland.