Can I Dunk My Pennies In Water?

you can dunk them in water, you just shouldn't. they will get green.

to CCF!

I would also get them out of plastic, as this will cause pvc damage (the green you may be seeing)

1. Do not clean coins
2. Take them out of the plastic bag. It possibly holds moist air which is not good for coins or any metal.
3. DO NOT listen to anyone that says to use Olive Oil, tap water, wire brushes, toothpicks, baking soda/water solutions, Lemon Juice, Tomato Juice and on and on and on with all the so called "I've tried this and it works" stories.
4. Separate the different types of coins so any Silver, Steel, Copper ones do not touch each other.
5. Your so called Silver looking PENNIESE are possibly 1943 Steel Cents plated with Zinc.
6. Eventually purchase either an Album or 2x2 cardboard flips for those coins. For now you could also use plastic Rolls but if you do, read 4. above.

The problem with tap water is it is different everywhere. In some areas people run it though a water softener which adds NaCl to the water. In many areas Chlorine or Florine is added to the water to kill bacterias and germs. Well waters contain almost anything on Earth and usually Iron.
Any or all of them will leave contaminates on your coins or even attack the metals of coins.
The above reasons are also why so many people have house plants that die. This type of water kills plants so imagine what it does to your coins and/or you.

NEVER clean coins unless you have professional training

You can clean them. You just probably won't like the aforementioned results that develop later on.

In reality pipes of old were Steel, not Copper. All the pipes in my house are Steel and my house is on the old side. Same with almost all old houses. Copper and/or plastic piping is rather new for water in houses.
AND if you ever replaced one of those old Steel pipes, you would probably get sick thinking about what you see in the inside delivering water to you. In many areas those steel pipes are almost completely closed by rust and stuff. And in many cases that is what people use for coins?

Using acetone is consider a conservation step and not cleaning. Careful use of water, acetone and xylene are all safe for coins. In this case, the OP was discussing a mass cleaning of his coins. This is a lot different than conserving a single coin with a specific problem.

In general, only coins with problems should undergo conservation and only by an experienced hand. Just telling someone to go rinse all of their coins would be irresponsible and inappropriate. You have to consider that most of the people asking questions about cleaning are novice collectors and chances are great they will ruin their coins forever by making a grave mistake.