BS 8515:2009 pdf free.Rainwater harvesting systems — Code of practice.
BS 8515 The detailed approach should be used to calculate the storage size more accurately for all situations and particularly where: a) the demand is iregular (e.g. external use, non-residential use, tourism); b) the yield is uncertain (e.g. due to the use of green roofs, permeable pavements); c) costly, larger or complex rainwater harvesting systems are proposed. NOTE 1 Computer models may be used to simulate the performance of the rainwater harvesting system as accurately as possible. The uncertainty associated with both the demand and the supply needs to be considered using appropriate uncertainty methods. To apply the detailed approach to sizing the rainwater harvesting system for non-potable domestic use, storage capacity should be estimated by building a model of yield and demand, which is based on a continuous rainfall time series for a minimum of 3 years and preferably 5 years. This time series should use daily rainfall data for assessing non-potable system storage. NOTE2 From an analysis of the results of using a time series for design, the frequency of overflowing can be found. Occasional overflowing allows any floating material to be discharged and offers potential benefits for water quality. NOTE 3 The analysis also enables an assessment of how much water might be saved annually and the number of days that no rainwater is available, which is particularly useful if there is no back-up supply. Where the system is to provide both non-potable water for domestic use and stormwater control, the integrated sizing methods detailed in A.3 should be used to estimate the additional storage capacity needed.
When selecting a collection surface, the following factors should be taken into account, as these can affect the quality and quantity of the collected water:
a) the surface’s materials and their drainage characteristics, e.g. run-off from a green roof will be significantly less than that from
a hard roof and is also likely to be affected by a colouration caused by the soil or fertilizers;
b) the levels of pollution and the risk of contaminants entering the system.BS 8515 pdf download.