The WaterSMART Access for Tribes Act amends existing federal water conservation law to make it easier for Native American tribes to access federal water efficiency and conservation grants. Currently, tribes must contribute a non-federal share of project costs to receive these grants, which can be a financial burden for tribal governments with limited resources. This bill allows the Secretary of the Interior to reduce or waive the tribal cost-sharing requirement if the secretary determines that paying this share would cause financial hardship. The change applies to water infrastructure improvements and conservation activities that tribes pursue under existing WaterSMART grant programs, removing a barrier that has limited tribal participation in these federal funding opportunities.