Window Cleaning Resource carries DI tanks and replacement DI resin which is essential in creating pure water for waterfed window cleaning. DI resin can be used as a standalone filtration system or it can also be used as the final step in a multistage purification system, such as any of the XERO Pure Water Systems for example. Your TDS (Total Dissolved Solids) plays a huge parts in determining how long your resin will last. If you have a higher TDS, the lower upfront cost of a DI only system may seem attractive but you have to consider how much faster you will burn through resin. A Multi Stage System costs a lot more up front but you will be changing the DI resin much less frequently and it will cost less. Bottom line: if you have a higher TDS the multi-stage system is a much better investment in the long term. However, if you have soft water or are an infrequent user, a standard DI tank, or other Single Stage System may be a suitable option.