Charles,  Frankly, there too many models, and it all depends on what you want to achieve from  these models. Have a look at these papers, in particular:

http://onlinelibrary.wiley.com/doi/10.1029/2010WR009624/pdf

http://www.iwaponline.com/wst/06707/wst067071634.htm

Many thanks Pradeep Kumar. for your link. I hope to model on the most cost effective approach to water supply system for my municipal in Nigeria. Such that it will assist in water planning and budgeting for households and things like that.... I will also cherish if you streamline the idea as well 

Charles, That being the case, see this link below:

https://www.researchgate.net/publication/229429889_Click_Here_A_hydrologiceconomic_modeling_approach_for_analysis_of_urban_water_supply_dynamics_in_Chennai_India

Article Click Here A hydrologic‐economic modeling approach for analy...

Dear Charles,

COST EFFECTIVE OPERATION OF URBAN WATER SUPPLY SYSTEM USING DYNAMIC PROGRAMMING

by

Mohammed Hossein Sabet and

Otto J. Helweg

and,

Cost-Effectiveness Analysis: Drinking Water Utilities in Belgaum City Corporation

by

 Sandeep M.S.

Divya Krishnaswamy

Centre for Budget and Policy Studies (CBPS)

Regards,

Vanessa

http://onlinelibrary.wiley.com/doi/10.1111/j.1752-1688.1985.tb05353.x/abstract

http://www.gdn.int/admin/uploads/editor/files/GDN_PEMRP_CBPS_CEA_Water.pdf

If you are looking more into a semi-arid setting your approach would be different to a much wetter Eastern Nigeria setting. You can check the following:

http://www.nwc.gov.au/__data/assets/pdf_file/0016/10933/44_Scarcity.pdf

http://www.rff.org/documents/RFF-DP-08-22.pdf

http://www.environment.gov.au/system/files/resources/a4c27c83-6edd-4fc5-84a2-70e38b183fc4/files/urban-water-report.doc.

 All the best

Thanks so much Michael Adelana. I will go through the link to access them. Best regards

Dear Charles,

follows the file,

Best wishes,

Vanessa