Gray water is an ideal water con­ser­va­tion method both in the home and in the com­mu­nity. Any wash­wa­ter that has been used in the home (except water from toi­lets) is called gray water. Dish, shower, sink, and laun­dry water com­prise 50–80% of res­i­den­tial “waste” water. This may be reused for other pur­poses; espe­cially land­scape irri­ga­tion which helps cut down on fresh water use and pro­vides nutri­ents to plant life.

How recy­cling gray water helps

• Lower fresh water use: Gray water can replace fresh water in many instances, sav­ing money and increas­ing the effec­tive water sup­ply in regions where irri­ga­tion is needed. Res­i­den­tial water use is almost evenly split between indoor and out­door. All except toi­let water could be recy­cled out­doors, achiev­ing the same result with sig­nif­i­cantly less water diverted from nature.
• Less strain on sep­tic tank or treat­ment plant: Gray water use greatly extends the use­ful life and capac­ity of sep­tic sys­tems. For munic­i­pal treat­ment sys­tems, decreased waste water flow means higher treat­ment effec­tive­ness and lower costs.
• Highly effec­tive purifi­ca­tion: If applied cor­rectly, gray water is puri­fied to a spec­tac­u­larly high degree in the upper, most bio­log­i­cally active region of the soil. This pro­tects the qual­ity of nat­ural sur­face and ground waters.
• Less energy and chem­i­cal use: Less energy and chem­i­cals are used due to the reduced amount of both drink­ing water and waste water that needs pump­ing and treat­ment. Also, treat­ing your waste water in the soil under your own fruit trees def­i­nitely encour­ages you to dump fewer toxic chem­i­cals down the drain.  How­ever, it should be noted that gray­wa­ter should not be applied directly to fruits or veg­eta­bles that are eaten raw.
• Ground­wa­ter recharge: The use of gray water recharges groundwater.
• Plant growth: Many times gray water includes valu­able nutri­ents that allow the land­scape to flour­ish; unlike drink­ing water that has been purified.
• Recla­ma­tion of oth­er­wise wasted nutri­ents: Loss of nutri­ents through waste water dis­posal in rivers or oceans is a sub­tle, but highly sig­nif­i­cant form of ero­sion. Reclaim­ing nutri­ents in gray water helps to main­tain the fer­til­ity of the land.

While the Mary­land state code (COMAR) defines gray water as sewage and there­fore not for re-use, the Mary­land Depart­ment of the Envi­ron­ment allows local juris­dic­tions to enforce pro­vi­sions of the State or National Plumb­ing Code the juris­dic­tion adopts.

In Howard County we have adopted National Stan­dard Plumb­ing Code 2009 edi­tion Appen­dix G which reg­u­lates gray water as defined at the top of the page (as opposed to the COMAR definition).

Mary­land House Bill 604 (This bill did not pass the Mary­land leg­is­la­ture this term.)