Recently, I asked readers to offer their ideas for how nonprofit groups can best use the social-networking site Foursquare.

Followng that post, we received a number of interesting ideas and I had the chance to connect with Joe Waters, director of cause and event marketing at Boston Medical Center.

Mr. Waters, who authors the blog SelfishGiving, has been a Foursquare early adopter and has been watching how nonprofit groups are starting to use the service as a way to connect with their supporters.

Below is his guest post about his experience with Foursquare—and his recommendations for how nonprofit groups can make the most of the site.

Just last month the location-based social networking service Foursquare emerged as the new social media darling at the annual SXSW Interactive Conference in Austin, Texas.

Foursquare was a huge hit and charity played a big role in engaging attendees. A partnership between Foursquare, Microsoft and PayPal to raise money for the Save the Children Haiti Relief Fund logged over 135,000 check-ins and raised $15,000.

The beauty of the location-based service is that nonprofits of all types and sizes can tap its social marketing prowess. Here’s how:

Nonprofit branding. The geo-location element of Foursquare is a great way to put your nonprofit on the map. My team and I check-in at my Boston hospital every day as a form of organizational branding. With 5,000 employees and more of them joining Foursquare every day, the potential impact of all those check-ins could one day be significant. But don’t just check-in. The tips and shout-out features on Foursquare let you include interesting details about your cause. For example, I could check-in at my hospital and post: “Heading over to the hospital’s Prescriptive Food Pantry, the only one of its kind in the country.”

Volunteer management. Every October we have a Halloween event with 1,200 volunteers, many of whom are smartphone-toting college kids eager to give back. This year, the volunteers who are also Foursquare users will check-in to their respective areas (e. g. Pumpkin Patch, Spooky Speedway, etc.). Not only will we know who is where but after they friend the volunteer coordinator on Foursquare we’ll be connected to them by phone and text so we can easily contact them.

Cause marketing. The Paypal, Microsoft partnership with Foursquare and Save the Children was a great example of geo-location cause marketing. Here’s another. Recruit a corporate partner to make a donation to your cause every time a Foursquare user checks-in to their store or restaurant. Another option is to tie-in a badge that users can earn after checking-in several times.

Event promotion and recruitment. I got an e-mail the other day asking about how walks, runs, rides and other types of athons might use Foursquare. The cause marketer in me is drawn to how corporate partners can promote athons to consumers that check-in on Foursquare at their business. “Join iParty at the Walk for Cancer this Saturday.”

Shopping fund raiser. If your nonprofit group is located in or near a shopping district, you can recruit a group of stores and restaurants to offer a weekend discount to Foursquare users. The lucky shopper saves 10% when they check-in and the store makes a donation to your cause.

These are just a few of the ideas I have for Foursquare. How would you use it?