Simple, do the frying pan test. Let a large frying pan get real hot on your stove. Make sure there isn't any water already in there. Then slowly CAREFULLY pour your recycled oil in, about half to one cup. Be ready to jump back. If you get hit by lot of jumping, hot tiny splatters, there is a lot of water in your oil. If there are air bubbles coming to the surface and you hear some popping noises, there is definitely a little bit of water there. No water is when the oil glides around the pan and you cannot see any air bubbles in the oil.
Don't let the heat stay on high too long unless you plan to heat the oil to make filtering time faster. If the oil is too hot, it will start smoking, burning badly.
Lots of people heat the water out of the oil, called de-watering. I place a farm coil heater, heats to a max of 120 deg F = 55C in with 20-30 gal of the recycled oil for 4 hours. You can hear the water evaporating to the top, pock,pock,pock.
If you find the drum lid slightly off the drum after a rainy night or a really foggy spell then the oil is risky, probably has much water in it.
If your source keeps the drum under a shelter, that is awesome!
If you can find a petro-filling style portable fuel pump, it is worth the price. I swear by it except mine is so heavy.

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Frankie
It never ends!
1985 300D Turbo 181K Anthracite grey, "SOPHIA"
1984 300 SD Turbo(sold)
2004 Subaru Forester XT,Cayenne red.