Wednesday, January 19, 2011

Under (Water) Pressure

Given the somewhat terrible water around these parts, and rather than spending a small fortune buying distilled water from a pharmacy (or begging it from people who have lab grade distillers or RO machines), I've been considering getting a fairly hefty Reverse Osmosis (RO) unit, not only for the benefit of the orchids, but also the fish (who currently get bottled water, as do the rats), and of course, the humans around OoaB.

When I asked for a quote and about the need (or otherwise) for a pressure booster pump, "The Waterboy", Marco Justino, based in Durban, said that this was not required as long as the incoming water pressure was over 3 bar.

I said I'd try and figure out a way of measuring the water pressure here and get back to him.

I spent a frustrating 30 minutes or so going around all the places that might conceivably have a pool filter pressure gauge. None did, not even the pool shop. Eventually, I thought laterally and wondered if I might persuade a car oil pressure gauge to work (at least briefly); a quick trip to Midas and R90 later, I had a gauge that could read up to about 7 bar. A few Gardena hose fittings on top, and I had what I hoped would be a workable water pressure gauge.

Oil pressure gauge and Gardena fitting
Conveniently, one of the fittings that came with the oil pressure gauge happened to be just about the right size to self-tap into the plastic of the Gardena fitting. Yay!
Ooer, it actually works!
Somewhat to my surprise, the jury-rigged gadget worked, and showed the pressure on the cold tap in the bathroom to be about 4 Bar (coincidentally enough to just pump a column of water about 40m into the air). Why the hot water pressure in our house is therefore so totally pathetic (taking a hundred years to fill the kitchen sink and giving us showers worthy of the worst in the UK, legendary home of pathetic water pressure), I don't know, but I suspect is has something to do with the geyser (immersion water heater) that looks like it was wrought out of lead, by gnomes at work deep in a mine, in about 1824.

So it looks like there's enough pressure for RO, yay, which saves about R800 on a booster pump. Still, given the fairly high TDS/EC, I wonder if a higher pressure might not be needed to force that water across a membrane?

Incidentally, I tested (pre calibration) the Oasis ozonated water available from the Oasis filtered water shop here, and it has an EC of about 8 - which will do for now. And at R4.50 for 5 litres, is a whole lot more affordable than R37.15 for 5l, or R13.75 for 1l that pharmaceutical grade distilled water costs!

Of course, I imagine that water and oil pressure gauges are not happy buddies, and I doubt that gauge will work again once its insides corrode...