RO Full Service Kit, 6 Stage

The three pre-filters change every six months, the post-carbon and re-mineraliser every year, the membrane every two to three years. Most years, the pre-filter kit twice plus the two inline stages once is the right shopping list. The year the membrane is due, or the year you inherit a system with no service history, buy this kit and start the clock again.

Choose the membrane above. The AquaShield ships with a 100 GPD membrane (378 litres a day at 4 bar), so an AquaShield service takes the 100 GPD kit and the system makes what it made on day one. Most other five and six stage under-sink systems in South Africa shipped with a 75 GPD (284 litres a day); the rating is printed on the membrane's label. Both are the same 1812 size and fit the same housing.

The last cartridge is four media in one body: maifan stone, mineral stone, bio-ceramic granules and far-infrared ceramic balls. The first two put calcium, magnesium, potassium and sodium back into the membrane's water and raise its pH; the other two are rated for a last pass at chloroform and heavy metals and for holding the pH steady. It is the stage that makes RO water taste like water, and on a five-stage system its clamps, elbows and tube make it the sixth. The re-mineraliser's page takes each medium in turn.

The three housings as for the pre-filter kit. The membrane: unscrew the long horizontal housing, pull the old element with pliers, push the new one in O-ring end first. The post-carbon: pull the tubes out of the old cartridge and push them into the new one, arrow pointing to the tap. The re-mineraliser: its own two compression elbows, the nuts tightened by hand onto the tube, arrow to the tap. Run the first two tanks to the drain to flush the membrane preservative.