i have got a small system with 125 litre tank and that the more that i use the less water i use as i am getting better at it, i used 125 lit today on 8 house bearing in mind 7 of these i do trad and are all 3 bedroom and 1 thats hadnt been cleaned in ages and had about 20 windows, need to get a bigger tank to help me but i cant be bothered yet, i remember readiing some where that you use 20 litres of water per house,