Here's the thing. Yes, you can use tap water. Especially in Van, the water is very soft and pretty good quality. You may get nutrients going into the tank to cause algae, you may not.
But with a water distribution system so large, the room for something going wrong, like introduced contaminates, is fairly possible. You wouldn't know it unless it was really bad (I remember Kelowna in 97 had to boil water for a few months) and there was a public announcement. But a mild issue, coming from a broken main near a gas station, could wipe out your whole reef. If' you've got a little nano with 2 corals, maybe you want to take that risk.
For me, I've got thousands of dollars worth of SPS. I'm not going to risk losing it all by using an unknown factor. Our water is really good here too, almost all of the time. But what if?
A RO unit is a couple hundred bucks, tops. Half that for used. I think that's a pretty good insurance policy.
In emergencies, I've used tap water for a water change. Nothing bad happened. No algae. But....what if just once there was a contaminant in the public water that was toxic to corals? That's not something I want to encounter!
Lots of people do it, and I guess it's personal choice based on what your corals are worth and the level of risk you're comfortable taking.
Also, keep in mind that household plumbing does contain copper, and can leech it slowly into your system.
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Brad
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