Terminalia chebula of Combretaceae family could be helpful in reducing ground water hardiness.

Ground water hardness can also be removed by using seeds of Moringa Oleifera , which is independent of pH and alkalinity of water.

 The most effective way to reduce the hardness can grow plants "duck weed". (Known as Egeria densa or water lens or bayroot. They are flowering aquatic plants which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands.)

Not sure what type of application you are looking but some links below:

http://pubs.sciepub.com/jaem/2/3/5/

http://www.academia.edu/11650214/REMOVAL_OF_HARDNESS_CA2_MG2_AND_ALKALINITY_FROM_GROUND_WATER_BY_LOW_COST_ACTIVATED_CARBON_USING_EICCHORNIA_CRASSIPES_PLANT

http://soiltesting.tamu.edu/publications/SCS-2002-10.pdf

http://www.amnh.org/learn-teach/young-naturalist-awards/winning-essays2/2012-winning-essays/using-plant-based-biofilters-to-purify-household-wastewater

http://www.fs.fed.us/geology/FINAL_Ground%20Water%20Technical%20Guide_FS-881_March2007.pdf

http://www.uwsp.edu/cnr-ap/watershed/Documents/dodge_gw.pdf

http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0013/164101/Farm-water-quality-and-treatment.pdf

http://www.lonza.com/~/media/Files/water-treatment/Weedbook.ashx?la=en

http://ag.utah.gov/documents/AquaticPestStudyGuide.pdf

http://www3.uwsp.edu/cnr-ap/weal/Documents/G3582.pdf

http://www.dec.ny.gov/docs/water_pdf/dietlakech6.pdf

https://articles.extension.org/sites/default/files/w/1/1d/Pond_Management_and_In-depth_Response_to_FAQs_from_Pond_Owners_and_Managers.pdf

http://cru.cahe.wsu.edu/CEPublications/pnw0224/pnw0224.pdf

http://www.stormwatercenter.net/Manual_Builder/Maintenance_Manual/9%20-%20BMP%20Maint%20Ed%20Materials%20and%20Links/South_Carolina.pdf

http://aquaculture.ext.wvu.edu/r/download/45846

http://www.ecy.wa.gov/programs/wq/pesticides/irrigation/fs-irrig_district-final.pdf

http://www.chesco.org/DocumentCenter/View/7737

https://fortress.wa.gov/ecy/publications/publications/0010043.pdf

https://ag.purdue.edu/btny/weedscience/Documents/Water_Quality.pdf

Thank you so much for your valuable answers

i try to use the Strychnos potatorum seeds. it was works for some extent. Dear Sakshi, Moringa Oleifera seeds can remove the CaCo3 but when i search the literature, it mention total hardness of the water cannot reduce due to releasing of MgCo3 from plant to water.

Agree with Mohan Thampi sir.

@ H K Nimalka Sanjeewani

Please take a look at this useful RG link.

Thesis Characterization of ground water hardness with special refer...

Thanks!

Hello, you can use microalgae to reduce ground water hardness.

Butea monosperma flowers used as tonpurify water as well its sacred plant several other sacred plants used as water purifiers like Ocimum sanctum in telangana state to remove excess floride and others

Following!