Hi,
I faced a not dissimilar problem during the recent drought over here. We use roof collected rainwater but no rain for 6 months all but ran us out.
Our forest dam had clear water around ph6.5. I pumped it into the 5000 gallon tank while adding pool chlorine (8 grams of granular pool chlorine (calcium hypochlorite - 65% available chlorine) per 1000 litres.
Enough chlorine should be added to provide a free chlorine residual of around 0.5 milligrams per litre (mg/L) after 30 minutes. As a general guide, an initial dose of 5 mg/L of chlorine will provide this residual. You can test the residual in your water tank with a swimming pool test kit or dip strips, which are available from pool shops.
After chlorinating, you should ideally wait at least 24 hours before using the water to allow for harmful microorganisms to be destroyed. The chlorine may leave a harmless taste and odour in the water, which should disappear in around 10 to 14 days. Boiling the water will remove most of this taste and odour.
If you expose the tank (top of tank off) to sunshine, the odour and taste will dissapate in a matter of a day or so. this is the route I took.
The water will be fit for human consumption, free of all bacteria, and clear.
If you wish to use your filters after that then away you go, else use it directly.
Most of the above info I lifted from this web site when i set mine up.
http://www.health.vic.gov.au/environment/downloads/your_private_drinking_water_supply.pdf.
So I did this until the rains came, and now back onto tank water from the roof. But the chlorinated, flocked dam water was crystal clear and safe as a house. 22000lts (500gal approx)lasted us about 80 days or so, then you do it again... etc.
it's dirt cheap, and provided no heavy metals or other nasty inorganic toxins are in the creek it will work. I would however get the local council authority to test the water for harmful agents first. If it's full of mercury or whatever, your back to square 1.
The first one i did, I used a pool pump and a zeolite sand filter, but the flocking agent actually does a better job.
I was going to try and use expensive filters, but this did brilliantly. You could see a pin on the bottom of the tank 8 feet deep. And after "sunning the tank" there was no sign of chlorine taste.
On one occasion, I tipped in more chlorine than I should have on the theory "more is better". Dont do it, it just takes longer to get the taste out.
Hope this will help
.......oztules