Rainwater harvesting ROI modelling

[Dan F]

Has anyone done modelling of any kind using past rainfall and evapotranspiration data to determine the ROI for differing sizes of rainwater havesting tank vs. a small mains accumulator.

 

I've found some fairly local past data for 2020 [1] and some interesting theory [2] that details a method that can be applied to model this.

 

For now I'm using a basic approach with a fixed number of mm irrigation per day, depending on the month (rather than simulating a control system that irrigates based on soil moisture/rain) but initial results show water usage of 360m3/yr with a small mains accumulator and 330m3/yr with a large 6800l tank.  If this is correct, the ROI is something like a couple of hundred years and that's ignoring additional maintaince to cleare/replace filters.

 

[1] https://crondallweather.co.uk/daily-monthly-and-seasonal-evapotranspiration-statistics-for-crondall/

[2] https://agriculture.vic.gov.au/__data/assets/pdf_file/0008/577025/What-is-evapotranspiration-and-how-do-I-use-it-to-schedule-irrigations-Tech-Note.pdf

Edited October 5, 2021 by Dan F

[PeterW]

Yep the cost of the tank and controls will far outweigh any ROI that isn’t measured in decades. Worth seeing if you have anywhere to “hide” IBCs as they are a cheap option - I’ve buried them before in steel cages and concrete capped them but you need to be sure they will work for you like that. 

[Dan F]

52 minutes ago, PeterW said:

Yep the cost of the tank and controls will far outweigh any ROI that isn’t measured in decades.

 

Well, I think we'll put a tank and controls in anyway,  the idea being garden looks after itself a bit more.  So I was only looking at the additional cost of larger tank (7,000l) and additonal associated excavation/muck-away vs. 3000l accumulator + additional filters etc.  But the large tank, if I've modelled it correctly, would only save £50/yr mains water as when you need to irrigate it typically hasn't rained, and a 7000l tank only lasts a few days in the middle of summer.

 

52 minutes ago, PeterW said:

Worth seeing if you have anywhere to “hide” IBCs as they are a cheap option - I’ve buried them before in steel cages and concrete capped them but you need to be sur

 

Will look into this, thanks!