Dumb question, sorry

Close to my land there is a well pumping water for both irrigation and human consumption. The water for consumption is being piped directly down to the village whereas the water for irrigation flows in to reservoirs which fill over time and once full, flow down an irrigation channel to the fields. My question is, is there any reason that the water being stored in the reservoirs would be any less suitable for consumption than the stuff being piped straight down? I don't know but I doubt the water stays much more than a day or two in the reservoir before it gets replaced. As a side note, all the water gets boiled before consumption.

The reason I ask is that I may have trouble convincing the local community to share their piped water with me whereas the reservoirs and well are only a few hundred meters from my land and could be collected without any problems. Can anyone think of any issues with drinking the reservoir water, what further treatment could be applied to sanitise it further?

I'm far from an expert on this, so I'll just point out you should check into the local laws about taking water from the reservoir and a sand filter and boiling would be my bare minimum for treatment. Water in any size open lake will be exposed to all sorts of contaminants including animal waste, soil bacteria, and chemical pollutants. Having said that, I also would point out that people have been drinking from open bodies of water since man has existed so it can be done safely.

Sorry when I say reservoir I mean a small affair, there are 2 concrete lined pits each with about 35,000 liter capacity. One fills up and then overflows to the second which then overflows to the irrigation canal. It's private, owned by the community itself. They are funny about the piped water but the irrigation water is readily available. I think the difference for them is logistics rather than potability, the piped water although with a smaller capacity (due to coming down a small pipe) can be received in a clean, orderly fashion. The irrigation water which they have in greater capacity firstly comes down a concrete channel to the reservoir but for it to reach the community it travels down a ditch for a couple of km and so gets contaminated - as far as they're concerned it's undrinkable. For me though living practically next to the reservoirs the water is still good quality. Well actually it may not be, that's what I'm asking

In the US, public water system sources are classified as either Groundwater, GWUDI (Groundwater under the direct influence of surface water), or Surface Water. Since you're taking from a reservoir, I would technically consider you a Surface Water system. Granted, you would be a relatively less risky surface source because they are concrete lined reservoirs fed only by groundwater. They are still open to some contamination. Boiling will neutralize bacteria and most microorganisms, but not cryptosporidium. To use this source safely , a state agency would typically recommend applying a disinfectant to kill bacteria and viruses (most commonly chlorine bleach below 4 mg/L), then running it through a 5 micron filter (not required, but extends the life of the more expensive 1 micron filter), then a 1 micron absolute filter. Personally, I am not a fan of chlorine, so I might just use a Berkey for the portion I'd be consuming.

I think there is some hard-to-quantify additional risk from contamination (bird drop, insects, algae, etc.). It's expensive to test for crypto, but a simple total coliform bacteria+E. Coli test at our State's lab runs US $17.50.

I would filter it, A sand filter at least.

I use these filters as they can be back flushed and last a long time.

http://sawyer.com/products/type/water-filtration/

This looks promising....at least a place to start

http://www.cawst.org/resources/biosand-filter