Ok where do I start, I would try to make this long story short by giving highlights and follow it up with my question.

• First time out of the parents house and rented with me
• HOA sent letters concerned that there might be illegal activities going on, confronted them, they denied any wrong doing.
• one of them was a smoker. I specifically asked, any smokers during the application process and they(3 of them) said NO.
• I inspected the unit every 3 months just to make sure things are on the up and up, most cases yeah. replace damaged blinds and replace light bulbs (not doing that again, they called because a light bulb was out after that. they are not kids mid-upper 20's with kids)
• The unit had 3 water leaks in the span of 3 month (grey pipes <sigh>. I have a post about this in another forum. look for grey pipes) 
• It was coming to the end of their lease and informed them that I would not be renewing the lease because I would like to replace all the water line in the unit by taking out the recalled pipes.
• rent has always late (7-10 days)
• water company always send a courtesy bill letting me know what the water bill balance is. balances was carried from quarter to quarter.
• Before they left, they asked for their security deposit (1 months rent) so they can use it as a deposit at the new place, i declined because it was meant for damages etc when they moved out.
• Gave them 6 weeks to find a place, the main lease holder moved out 3 weeks into the 6 weeks without informing me. i sent numerous notices for the main lease holder to let me know 5 days before vacating so we can do a walk thru, never did.
• On day 5 of their last month, I asked for the rent, and was told they would pay when they move because they do not know when they would be leaving. I figured there is nothing much I could do, i cant evict them (court paper work etc), they are on their way out. on day 5 they said they are sure they wont be there any longer than day 19, when day 19 came around that was when I found out the main lease hold left on day 12, leaving the other 2 there. Informed them the clock is still ticking until I get the keys. so the other 2 left on day 22. I was there that morning to collect the keys, and they still left  bunch of junk which i had to toss out after numerous notices for them to pick them up.
• at this point i had no choice to use their security deposit to cover that months rent, and am sure that was their intention, not paying and using the deposit as rent. So I prorated for the 22 days + damages = deposit + approx $160. Now they owe me about $160. Not sure am going to see that, I am willing to write that off.
• Now they left a hefty water bill of about $700 and light bill (amount unknown, company will not disclose since it not my bill owner, but I was told it's HUGE, I figured between 700-1000. did a i little guessing game untilI was in the ball park). Every time I visited the electric furnace is constantly on high, even when they go to work (LOL). thats another story. they swapped out my 7 programmable thermostat for a non-programmable one...go figure. was told it was too complicated.
• electric bill are individual bill and water bill (although in the tenants name) is still tied to the property because it's a city service. 
• Now am stuck with the water bill. I do not mind paying it because my next tenant would need to turn the water on in their name, and can't do so with a previous balance.
• How can i collect on this, either thru wage garnishment or have a collection company do the dirty work of collecting. 
• BTW, when they were signing the lease they also agreed and signed a letter on my intent to report their paying habit either good or bad to a service called  tenantverification.com, hoping they would want a good record by paying on time and not leaving any bad debt behind.
• I live in Maryland
• SO HOW CAN I COLLECT?