Under the feed-in tariff (FiT) scheme for renewable electricity generation you get a payment for every unit of electricity generated from micro-hydro power, whether you use it yourself and save on bills or export it to the grid.
How much electricity you can generate will depend on the capacity of the turbine (in kW) and how many hours per day (or across the year) you can run it for.
From 1 January 2017, systems of up to 100kW capacity receive 7.63 pence per kWh.
For larger schemes see the full lists and updates for FIT rates on the Ofgem website.
In addition, any generated electricity that you use in your home will save you about 16p per kWh (what would otherwise be bought from the grid).
And you'll also get a small export tariff payment, currently 4.91 p/kWh (for small schemes this is often paid for 50% of total generation, rather than metered).
For a 5kW hydro scheme, this could work out to annual payments of thousands of pounds, guaranteed for 20 years.
Previously, to be eligible for FiT income you had to use installers accredited through the Microgeneration Certification Scheme (MCS), but now you need to seek accreditation through the ‘ROO-FIT’ process, via Ofgem. See the Ofgem website page on ROO-FIT or email them on ROOFIT@ofgem.gov.uk for advice.