(Cut and pasted from an earlier reply)
You'll also likely need a Reverse Osmosis (RO) with a DI unit.
You can buy these from RO Man, (the unit in the link bellow would probably suffice), depending on how much water you plan to use. Doing 'tops only' I use around 100 to 150 litres per day (it's four litres to a gallon by the way, although Wavie Davie can be far more precise with the measurements
).
http://www.ro-man.com/shop/product_info.php/cPath/22/products_id/30You'll also need a pole. I suggest an 18" one if you're mainly doing 1st floor windows. You can get these from numerous places, but this site generally gets a good rating and has an excellent 'frequently asked questions' area which explains just about everything you need to know to start using a WFP.
http://www.gardinerpolesystems.co.uk/You'll also need a static tank, I use two 200 litre water butts, at least six 25 litre water barrels and a hand-held TDS meter (£13 approx).
Also, don't forget to ask lots of questions here. I'm definitely not a WFP expert by any means.