One way of being environmentally friendly is to collect and re-use rainwater.
To be economically viable significant volumes of water need to be harvested. The volume available can be calculated by using the local weather data to assess the average rainfall for your area (in millimetres / month / square metre) and multiplying this by your available surface area (roof car park etc.).
The available water is collected into a storage tank which is sized to meet the typical maximum volume in say 24 hours and then water is transferred from the initial tank via a treatment system into a bulk storage tank.
A typical treatment system would be a primary self-cleaning filter and UV disinfection which will then feed the storage tank. The water in the storage tank may then be circulated through a secondary filtration system and disinfected with either UV or chemical treatment.
The treated water may then be used for many process uses and if suitably tested and monitored also for potable use.
Additional treatment may be necessary for process applications such as softening or for higher purity water, reverse osmosis.