Unfortunately there are currently no grants available for domestic rainwater harvesting systems. For other eco ideas, the Low Carbon Buildings Programme (www.lowcarbonbuildings.org.uk) is a government-funded grant scheme that can assist householders with the costs of installing domestic scale microgeneration technologies, including solar water heating, solar electricity (PV), wind turbines, hydro electricity, ground source heat pumps, wood-fuelled boiler systems and automated wood pellet stoves. There is also a possibility that additional grants for microgeneration or energy efficiency measures may be available locally to you. Your local Energy Saving Trust advice centre (call 0800 512 012 for your nearest one), or local authority would be able to advise you on this. Your local authority would also be able to advise you about any planning constraints in the area you are building in. Grow Your Own Energy (www.growyourownenergy.co.uk) offers impartial advice on which of the above microgeneration technologies would be most suitable to integrate into your new home and can also refer your details to reliable installers for free quotations. It is worth noting that it is virtually unheard of for grants to be awarded retrospectively. You should always obtain quotations first (bearing in mind that many grant schemes require the use of an approved installer), then apply to the appropriate grant scheme when you have decided which is the best quotation and finally, after receiving grant approval, start the installation work.