What is BS EN 15204 — Water quality about? 
BS EN 15204 describes a general procedure for the estimation of abundance and taxonomic composition of marine and freshwater phytoplankton by using inverted light microscopy and sedimentation chambers, including the preceding steps of preservation and storage.
Many of the general principles of the approach described may also be applied to other techniques of enumerating algae (or other entities) using a (conventional) microscope, some of which are described in Annex E.
BS EN 15204 does not cover field collection of samples or the analysis of picoplankton, quantitative analysis of free-floating mats of Cyanobacteria or specific preparation techniques for diatoms.
Who is BS EN 15204 — Water quality for? 
BS EN 15204 on the Water quality are useful for: 
- Wastewater collecting systems 
- Wastewater treatment plants 
- Plants treating industrial wastewater 
- Water supply treatment plants  
Why should you use BS EN 15204— Water quality?
Investigations of phytoplankton are an important part of marine environmental monitoring. Phytoplankton responds rapidly to environmental changes and monitoring of occurrence, species composition and biomass may therefore in many cases be used to characterize the environment and the degree of impacts.  
enumeration of phytoplankton using inverted microscopy
BS EN 15204 guides sampling, preservation, and storing for analysis of marine phytoplankton.
BS EN 15204 provides you with apparatus, sampling, transport, storage, and preparation of test pieces, preparation of reagents and apparatus, pre-treatment of test pieces, test procedure, and much more for enumeration pf phytoplankton using inverted microscopy.
The test methods and procedures provided by BS EN 15204 assist you in getting complete information for the enumeration of phytoplankton to insure ensure reducing the risk of severe health issues.
With obedience and compliance to BS EN 15204, you can enhance the efficacy of the water and manufacture a standardized product. 
