Wastewater is a useful resource that, if harnessed properly, can bring a lot of health and economic benefits, increase food production, reduce poverty, enhance fishing, tourism, rural and urban livelihoods. Here are a few points to note:

Irrigation and Agriculture:
Stormwater, urban runoff, and effluent from animal farms can be captured for irrigation and other farming needs. This kind of wastewater is usually high in nutrients (nitrogen, phosphorus, potassium, micronutrient, organic matter), and farmers love it. They can save on fertilizer costs and also preserve surface water and underground water that they would have otherwise used.

In the US state of California, 31% of reclaimed water is used for crop or landscape irrigation. In Mexico, most of the wastewater from Mexico City is used in irrigation districts surrounding the city, notably the Tula valley.
Note that sludge from treatment sites are also used in composting sites and also sent to rural agricultural fields.

Energy and Construction:
The waste materials (sludge) collected from a treatment plant can be biodegraded in a controlled environment and then combusted (burnt at high temperatures) to release Methane (A gas similar to natural gas). This can be used in boilers at homes and in buildings, as well as for cooking and heating purposes. Note that this digester kind of biodegrading can contain contaminants, and so the process has to be done properly. The sludge from treatment plants can also be combusted to produce electricity.
Note that there are different types of sludge. Sludge could be fecal (from human and animal poop flushed down the drains) and regular sludge, from rubbish and garbage that get into drains and sewage systems. Fecal sludge is high in contaminants and must be treated well before discharge.

Household:
Smart thinking by rural and urban dwellers can offer some real benefits to households too. For example, water use in the kitchen can be collected and used to water flowers and lawns. A couple of gallons each day means a significant saving on the water by the end of the year! Families can also reduce the amount of wastewater they produce by smart use of bathrooms.