Gauteng Smallholder Dec 2016 / Jan 2017 | страница 9

MAILBAG ‘How do I calculate evaporation, simply?’ S IR ~ I attempt to conserve my household's grey water for eventual use on my garden. To this end it flows through a simple gravel and sand filter which removes any fats and solids (and also deodourises it) before entering a lined “dam”. This is a circular dished affair about 15m in diameter, lined with a single sheet of thick greenhouse plastic (and therefore, hopefully impervious), over which is laid brick embedded in sand and grouted into position. The hole in which this is dug is of solid ouklip, of such impermeability that when it rains a hole dug in ouklip will take days, literally, to drain. The sides of the dam are gently sloped downwards towards the centre where the dam is about 1,2m deep, the idea being firstly to maximise the surface area of the water to enable as much of the sterilising interaction of the U-V rays of the sun as possible, and secondly to facilitate the exit from the water of any animal or human who should stray into its murky depths. I have had this ifor a few years now and in the early days it would fill to the brim, and even overflow after rain. This year, however, it is far from full, even after the recent rains, so much so that there's not enough in it to use for watering the garden. I should add that in the past year I have added a small solar pump to the set up which, during sunlight hours, pumps a steady stream up into the filter, discharging back into the dam and creating a pleasant tinkling sound, aerating the water a little and keeping the medium of the filter, hopefully, in an anerobic state. I should also add that our The Editor welcomes your letters, comments and opinions, but reserves the right to edit and shorten as necessary. Senders’ names and addresses must be included. Afrikaans letters will be translated. Post mail to: Letters, PO Box 14648, Bredell 1623 or fax [phone] or e-mail [email protected] 7 www.sasmallholder.co.za household's water usage has greatly decreased over the past year as our now-adult children have one by one moved out of our home. At most, therefore, we use 200 litres a day of recyclable water. My question, therefore is this: how much moisture does one lose through evaporation here on the Highveld? I ask, because I really can't believe (at least I fervently hope) that the dam and its Continued on page 8